I feel sorry for her baby too :(
her expectations are so out of line. In order for him to "behave" she'll have to browbeat him, exactly as someone else posted.
Or if he is a typical three-year old she may have forgot what she said to you.
Your ds sounds like a VERY well-behaved three year old. I'm sorry you had to deal with such awful people. Is it possible to limit your time with them?
Our contacts with family were limited because we live far away and it was a good thing. Our families were still horrible

but at least we didn't have to hear it all the time.
I just want to repeat that your ds sounds like a true sweetheart and I'm sorry that you had to hear such negative things. You are doing a great job parenting him.