First of all, the court order is between you and your husband. You XSIL has nothing to do with it. I understand that in-laws love their family. But clearly your XAH is a detriment to the safety of your child at this time. I might try to gently tell XSIL this and let her know that once XAH gets some help and recovery time under his belt that you can work on an amended schedule.
When I leave my ABF, I will also have to deal with these types of problems. It is so tough and you just wish that the other side can see how you have been affected. Somehow it is always about the A and the consequences of his actions and the A's family enabling and not understanding that there have to be repercussions.
HUGS. You WILL get thru this.