DS is 4. The 2 examples MIL gave for her concern were:
1. DS went on a walk with FIL and our dog. FIL gave DS control of the leash but then saw dogs coming and told DS he needed the leash back to keep him and the dog safe. DS shouted "NO!" and grabbed the leash back. FIL firmly insisted on handling the leash and DS sat down and had a tantrum. After a minute or so he got up and peacefully continued the walk with FIL. (I was not there, this came 3rd hand from FIL to MIL to me).
2. DS went on a walk with MIL (2 weeks later) and his older cousin on a path that goes right by her house. DS decided he was tired and hot and wanted to go back. MIL said he needed to stay with them and that they would go home soon (DH and I had just left them and started walking back to MIL's house). DS just said he was going back and started walking back to the house. MIL said he needed to run and catch up to DH and I on the path. He didn't catch up to us but walked in the house at the same time we did through a different door so he must have been just behind us on the path.
So, those were the 2 examples she gave for being concerned that DS has an issue with respect and she's very concerned about him. She also has made multiple comments about how it's not ok for him to say "No" to her or FIL (especially regarding the dog walking incident).
Before and after each incident I talked with DS about respecting FIL and MIL. I told him if he disagreed about something he had 2 options: talk it over peacefully or just do it. I also explained that it was their job to keep him safe so they got to make the final decisions. After the dog walking, he ended up apologizing to FIL. After his walk with MIL (2 weeks later) I told him he would not be able to go somewhere with MIL alone next time as a consequence.
Please give me some objective feedback here!