Well laws vary from state to state, and I also think it depends on what type of court order you have. If it is a protection order because he is violent/physical with you, then I would say he has to have the sister-in-law pick up your child. If its just a general agreement because all the parties (you, your ex and the OW) don't want to deal with each other, then you may have to let him pick them up. It might be best to take it to court and/or mediation unless he is physicall violent. Then I wouldn't deal with him at all.

If I understood my attorney correctly, as long as we both agree, who cares? If it is OK with both of you that he picks up the kids, then why would anyone else care? If it were to become a problem for you, you could then refer back to the written agreement and that would be legally binding.

I'm with Becky if you two can talk and come to an agreement then just do it. You can also make a plan where he would pick him in a separate place, not at your house. In a public place.