Kylie Jenner, Blac Chyna, Kim K All One Big Happy Family

They were once mortal enemies ... and now Kylie Jenner and Blac Chyna are joined at the hip, singing "I Don't F*** With You" at a Kardashian shindig.

Kylie, Chyna and Kim formed the girl group for Khloe's 32nd birthday party in Hollywood Monday night at Dave & Buster's.

As you know, Kylie's boyfriend, Tyga, is Chyna's baby daddy and the friction has been palpable, but apparently not any more.

Just as significant ... Kris Jenner was there, which means -- with Rob and Chyna's new show -- it's money making time.

Greenbacks are more potent than blood.