Re: Would you give up?
This is why the general recommendation is to not take kids older than your youngest. These behaviors are not at all unusual for foster children and really not even extreme. Nothing compared to the stories we hear in our training. I know someone who has a bio son who does the same thing to his little sister (even same car scenario). Yes, the boy has issues, but just know this is not that unusual of behavior. In your circumstance, you do have your own son to protect, but just know the agency probably won't be very pleased to move him "just" for that and depending on the need of your agency, may prevent you from getting other placements. JMO, of course. I hope you can get it resolved one way or another.
A SAHM to four long out of diapers (all used cloth for all or part of their diapering years) and a baby girl currently in cloth part time.