J and C-sounds like a very challenging, complex family situation. JMHO, but given you have 2 adults in your family and 2 older children I think you can all make your own decisions about if/when you see your parents. I realize it may be more difficult for you as it is your parents. You can only do what you think is best for you-as it is their behaviour and comments that are out of line and they seem unwilling to change.
If any of you decide that you would like to visit with them, is it possible to do a brief, occasional visit to their place so if/when or even before it gets uncomfortable it is easier to leave and avoid the scene of asking them to leave your home. Good luck with whatever you decide - and given all your efforts in the past( in my opinion) it would be perfectly reasonable to say you can't squeeze in a visit before May 1.