My father was hyper-critical of my parenting, now he's just mildly critical, but one time he started insulting my parenting style at the dinner table on Thanksgiving (with 20 family members there). I didn't say anything, I got up got our stuff, and started putting on my daughters coat she was 2 or 3 at the time. My dad says "where are you going" I said "home" he said why "I said you are done insulting the way I parent" and at that I turned around, made my apologies to the whole family and left. Of course my mom ran out begging us to stay and my dad came out to say he did not mean anything by it and to please stay, and I told him "Your actions have consequensces, I am 37 years old and you feel the need to belittle my parenting in front of the whole family, I want you to go back in there and you can explain it to all of them", and I left, it was the best thing that ever happened in our relationship, it changed the dynamics of our relationship.
I don't know these people but in many of the same situations I simply say, "that hurts my feelings", I know some people will say of no offense or your being to sensitive, but when you reply with "I cannot help how I feel, and what you said hurts", I believe they will modify their behavior after 1 or 2 times.
This biggest problem I see in your situation is the proximity of everyone involved, we live 2 hours minimum away from all our family, which means we only get extensively pre-planned support or emergency support, the distance is a blessing and a curse for us.
Also I want to suggest a book "Dealing with People at their worst" by Dr's Brinkman and Kirschner, I got this book when I became a supervisor the first time, it helped me alot then, and it helps to reread it every so often to polish your people skills.
I hope some of this helps,
Best of luck,
Bill