Whitney Houston's brother and sister-in-law arrived in Los Angeles yesterday to attend Clive Davis' big pre-Grammy bash ... a bash Whitney's mom called "obscene."

Whitney's mother Cissy slammed Davis' invite, saying, "I got an invitation to the party, which is the most obscene thing. I don't know why they would want me to come to the party in which she died, you know? I guess maybe he just sent me a copy for remembrance sake."

Whitney's brother Gary -- along with his wife Pat (who was also Houston's manager) -- begged to differ and flew into LAX Saturday, telling us they were going to "support Clive."

Houston was found dead in her hotel room this time last year, just hours before Davis' annual party just floors below.

Whitney Houston's daughter Bobbi Kristina and her BF were double-teaming a hand-rolled cigarette in Atlanta yesterday ... almost one year to the day Whitney died from a drug overdose.

It's unclear what's inside the rolling paper -- but c'mon.

It's interesting, considering Whitney's mother Cissy Houston has been vocal about her concerns that Bobbi Kristina could follow Whitney's path into drug abuse unless she drastically changes her life.

Bobbi's been at war with her grandmother for months ... and recently slammed Cissy for writing a tell-all book about Whitney.

Whitney passed away on Feb. 11, 2012 after going on a drug binge that included coke, pills and marijuana.

Bobbi Kristina is on a mission to make sure grandma Cissy Houston's new tell-all book crashes and burns -- by BOYCOTTING it altogether and pleading with her fans to do the same.

Cissy released a book this week called "Remembering Whitney" -- which is all about Whitney Houston's life -- and made the rounds on a slew the talk shows promoting the hell out of it.

But Bobbi wasn't too happy, tweeting to her 119,000 plus followers, "Anything concerning my grandmother's book, I and @nickgordon of course personally have nothing to with."

She continues, "I haven't read and won't ... I find it to be disrespectful to my mother and me being her daughter won't tolerate it."

FYI -- Cissy was on Oprah earlier this week (again promoting the book) and admitted her relationship with BK was strained ... and admitted she knew that Bobbi didn't want the book written.

Whitney Houston's brother says HE'S to blame for introducing the singer to drugs like crack cocaine back in the '80s ... not Bobby Brown ... and last night he came clean to Oprah.

Michael Houston sat down with his mother Cissy and spilled his guts to Her Royal O-ness on "Oprah's Next Chapter" ... admitting he was the first person who did drugs with Whitney. 

Michael says he feels extremely guilty for Whitney's death -- but says he didn't realize how deadly drugs could be when he first brought them to Whitney's doorstep ... explaining, "You gotta understand at the time ... the '80s ... it was acceptable."

Houston adds, "It's painful ... I feel responsible for what I let go so far."

Whitney died in Beverly Hills last February after a drug binge that included cocaine, Xanax and marijuana.

Bobbi Kristina's grandmother Cissy Houston has BACKED OFF her attempt to keep Whitney Houston's money from Bobbi Kristina for years -- we found out Cissy has settled her beef with BK.

TMZ broke the story ... Cissy and Pat Houston (co-executors of Whitney's estate) ... had filed legal papers hoping to drastically change the way Whitney's fortune would be paid out to 19-year-old Bobbi .. because they felt it was "too much, too soon."

As it stood, BK was to receive her money -- an estimated $20 million -- in 3 separate chunks ... 10% when she turns 21 ($2 mil), just under 20% at age 25 ($4 mil) and the remainder when she turns 30 ($16 mil).

Now, we've learned ... the case has been dismissed after Bobbi and Cissy reached an agreement ... and sources tell us Whitney's original plan for the payout was virtually unchanged.

Still, we're told both Bobbi and Cissy are satisfied with the plan ... and are happy to put the case behind them.

Whitney Houston's mother Cissy is deathly afraid Bobbi Kristina will die just like the singer -- in a haze of drugs and other bad influences -- which is why she wants to withhold Bobbi's multi-million-dollar inheritance, sources tell TMZ.

Sources close to Cissy tell us, Cissy feels Bobbi is currently surrounded by numerous negative influences -- including her boyfriend Nick Gordon and father Bobby Brown -- who will drain Bobbi's fortune given half the chance.

We're told Cissy also feels 19-year-old Bobbi is still extremely impressionable right now -- and if left unchecked with millions of dollars, Bobbi could end up going off the rails ... eventually dying just like Whitney.

According to sources, Cissy wants to wait until Bobbi has matured significantly more before she gets her money ... an estate estimated at $20 million ... though it's unclear how long she wants her to wait.

As for allegations Cissy is trying to withhold Bobbi's fortune to hoard the money for herself -- Cissy is telling friends that's total BS ... that it's about protecting her family.

As we reported, Cissy and Whitney's sister-in-law Pat Houston filed a request this week to modify Whitney's will -- in order to change the distribution schedule of the estate.

Whitney Houston's family wants to put the singer's fortune on lockdown to stop Bobbi Kristina from blowing her inheritance ... and to protect BK from financial leeches.

Cissy Houston and Pat Houston, Whitney's mom and sister-in-law, filed a request this week to modify Whitney's will. Specifically, they want to change the distribution schedule of the estate ... estimated to be worth at least $20 million.

Sources close to the family tell TMZ ... Cissy and Pat filed the documents because they think the current will gives BK "too much too soon" -- and they don't think she has any need for that kinda cash now.

We're told the family also wants to "protect [Bobbi Kristina] from herself" ... because she's vulnerable. In the documents, they claim 19-year-old Bobbi "is a highly visible target for those who would exert undue influence over her inheritance."

Bobbi Kristina, Whitney's sole heir, is currently scheduled to get her inheritance in three chunks -- 10% when she turns 21, just under 20% at age 25 ... and the balance when she's 30.

In their petition, Pat and Cissy don't mention what specific changes they are seeking to the current payment schedule -- but they say Whitney's intent was "to provide long-tern financial security and protection" for her daughter.

For the first time since Whitney Houston's death, her ex-BF Ray J has returned to the hotel where she died back in February ... TMZ has learned.

Ray J -- who was one of the first people to arrive at the Beverly Hilton Hotel on that fateful day -- had avoided returning to the hotel for months because it was "too hard" for him to return to the scene.

But today, Ray J had to overcome his fears to do a scheduled media event at the hotel for his new TV project, "The Rickey Smiley Show" ... an event he couldn't afford to miss.  

Sources close to Ray tell us ... the singer was overcome with emotion when he arrived to the hotel ... telling friends "it hurt inside" to have to relive his most painful memory. He also said it was "very weird" walking the halls again.

Still, Ray J is telling friends ... Whitney wanted him to do well and would be proud of him.

Cissy Houston was not happy this weekend when she was booked at the same hotel where her daughter Whitney Houston died ... but she does want to visit her daughter's death room at some point ... TMZ has learned. 

Whitney's mother is in Los Angeles this weekend for the BET Awards (where Whitney will be honored) and we're told she felt uncomfortable when she was set up at the Beverly Hilton -- the same hotel Whitney passed away in back in February.

Our sources say Cissy does want to visit room 434 for closure and is planning to contact the hotel this weekend ... but that she wants to do it on her own time.

According to our sources, Cissy's reservation was moved to the Regent Beverly Wilshire instead.

Whitney Houston's mom is pulling a Joe Jackson -- cashing in on her child's tragic death ... that's what some family members think of Cissy Houston's plans to write a tell-all book.

Sources close to the Houston family tell TMZ ... Cissy's new publishing deal with Harper-Collins for a memoir is merely a lame attempt to make money -- since Whitney left everything to Bobbi Kristina -- and not at all about honoring the late singer.

One source said the book -- which is slated for release next year -- could also be a PR move for Cissy, claiming ... "She will try to come out looking like the world's greatest mom, when in actuality, she wasn't."

Bobbi Kristina won't be prosecuted for gambling underage at a Vegas casino last month -- TMZ has learned the cops have closed the case due to insufficient evidence.

TMZ posted the video -- showing what appears to be 19-year-old Bobbi Kristina gambling at a slot machine with her 22-year-old boyfriend, Nick Gordon, at the MGM Resort and Casino. The legal gambling age in Vegas is 21.

As we reported, the incident was investigated by  the enforcement division of the Nevada Gambling Control Board, but Deputy Chief David Salas tells us, "We have completed our investigation and there is not enough evidence to support criminal charges." 

Salas adds, "We are going to close the case."

We're told the MGM was very cooperative with the NGC during their investigation.