My guess...
The cartels thought they were drug buyers.
They kidnapped two to hold for ransom.
They killed two to show they were not joking around.
The ones that were killed were male, so I’m guessing they tried to fight their way to an escape, maybe to let the females have a chance to leave.
If I wanted to have a medical prodecure done, I’d go to Spain. It’s almost as cheap and much safer than Mexico or the Philippines even.
Americanos negros stick out like a sore thumb en Mexico which is not a diverse place.