Florida Realtor, Ex-Husband and Young Daughters Dead in Apparent Murder-Suicide

A Florida realtor, her ex-husband, and their two young daughters are all dead ... in what police are calling a murder-suicide.

Law enforcement responded Tuesday to a welfare check at a Doral home and found Melanie Hyer, Ryan Whiten and their daughters Savannah and Sienna dead, according to the Miami-Dade Sheriff's Office.

MDSO says all four had stab wounds and they believe the tragic incident is a murder-suicide ... but no word yet on who did the stabbing.

Cops also didn't say who called in the welfare check and why, but former NBC6 investigative journalist Willard Shepard -- who was also Melanie's close friend -- says neighbors told him Savannah and Sienna were riding bikes Sunday with their dad.

Shepard recalled the last time he spoke with Melanie, saying ... "I talked to her probably a month and a half ago, no sign or any indication of something like this, and obviously if there was some sign of that not only would I have said something but taken some action but there was simply nothing that gave me any indication that this could have potentially occurred."