It's a difficult time for kids when they are going back and forth between families. My sons did it, and I also had stepchildren who went back and forth. It's common for the kids to become pawns, and for the extended families to treat them poorly and/or pump them for information, just to keep the toxic situation alive and well.
I let my kids talk things out when they got home. Only you can decide if it's truly harmful and detrimental, and if you need to call someone at Child Services, then do so. My warning/suggestion would be to do it with a pure heart as once that call has been placed, everyone's actions and agendas are under scrutiny, including your own.
Since your child is disabled, does he have a counselor or an advocate who helps with the care? Perhaps he could talk this thru with that person.