WHITNEY HOUSTON’s son-in-law is out of control – and now a source says the late singer’s family wants him dealt with harshly for appearing to threaten family members’ lives!

Nick Gordon, 24 – whom Whitney took in and raised as a son – married the “I Will Always Love You” singer’s daughter, Bobbi “Krissi” Kristina, 21, in January. And that didn’t sit well with her family!

Krissi’ Uncle Gary, Aunt Pat and grandmother, Cissy, were all said to disapprove of the union because they felt that Krissi was too young to get married and that Nick was only using her for money.

And while Krissi’s been lashing out at her family since her mother Whitney tragically died in a bathtub at the Beverly Hilton hotel in February 2012, sources say that even she thinks Nick may have gone too far this time.

On March 16, Nick appeared to tweet a reference to “Nightmare on Elm Street” killer Freddy Krueger, apparently to Pat Houston, and called her a “b****.” He appears to have directed other obscene rants at Whitney’s cousin Gary Michael Houston, and menacingly posted pictures of an AR-10 custom rifle with a scope attached, as well as a case with four handguns.

“Krissi has relied on Nick since her mom died, and her family has fought her about him because they never liked him,” revealed a family insider. “But now some of the horrible things Nick has posted on Twitter are beyond crazy. Krissi is still angry with her family, but she loves them very much and doesn’t want anything to happen to them.”

This isn’t the first time Nick has used a weapon in a threatening manner. In 2011, he allegedly pulled a 9mm semi-automatic pistol on several of Krissi’s friends during an altercation in a gas station parking lot in Roswell, Ga. Police later recovered another gun and ammunition from the glove box of his car. A source says that Gary, Pat and Cissy are now calling for legal intervention – and Krissi is desperate to smooth the situation over before it escalates even further.

“Krissi knows Nick has a bad temper, and he’s bent on getting revenge,” the insider added. “She’s afraid of what might happen next.”