Where is your son the other 3 days?
Not a good situation for your son to be in if he if not attended to. Children are like sponges and they will pick up and imitate good and bad behaviors. If your son is not getting the attention that he needs at such an important developmental stage, he can start "acting out". It would be best if your son was at the other childcare because of the consistency in routines and the ages of the other children.. His development is not being fostered and stimulated in a positive way with your in laws.
Hope this provides you with some insight.