Ray J & Princess Love Have Big Sis Headlining Their Wedding Day!

Ray J and Princess Love didn't have to look far to land a Grammy winner to sing at their wedding ... cause it runs in the family.

We're told big sis Brandy will sing Etta James' "At Last" for the couple's first dance. Check out the vid ... she's practiced before and nailed it.

There's more ... we're told Grammy winner Anthony Hamilton will serenade Princess Love with "The Point of It All" as she walks down the aisle.

But don't wait for a formal invite -- we're told the nuptials are going down next week. Brandy's pulling double duty ... she's also a bridesmaid.