I too have that problem. My dad and step mom are not being very nice right now either, I am thimking about saying
A tremendous day in our lives is drawing near
we the families of
blah
and
blah
would be honored if you would share ........
etc...


since more then just our parents are helping us with our wedding also, such as his brothers and sister in laws, my aunts etc.. that way everone is recognized but noone knows that certain people are being left out>