I think that in the end, the realy problem of situations like this is not "what people think about us" or that they are basically acting like school yard bullies..

It is that they are belittling us as parents in front of our children, undermining us.

That is simply unacceptable - and IMO requires the family member to vocalise their need to Shut Up!

Blunt, but J Man needs to tell them to pull their heads in because its destructive to your family and if they continue you will have to consider what is best for the emotional and mental welfare of your children, and that may be not going to see their aunts, uncles and grandies.