I have a similar problem with my mother and stepfather - but actually more severe. Because of this I have analysed it to death. If people fall out this much when everybody is trying to do the 'polite grandparents visit' (and, believe me, I have ejected my mother from my home and not spoken to her since April and I really don't care if I ever do again) - then there is usually an underlying problem that hasn't been got past.
I don't recommend you fall out with them - it is really upsetting in the long run and, of course, the children do not get the benefit of their input which is not the best for anybody.
BUT - and this is really important...sometimes that input can be negative and if it is willfully intentional then I agree - their input is not required.
A lot of people have this idea that you MUST be involved with your relatives and I really don't know why they think this. If you are all adults and they are deliberately treating you badly - you don't have to put up with that.
However - if you can get on and put aside your differences then you could benefit from the extra support.
You just have to weigh it up - are they making you more miserable than helping?
In my case they definitely were making us more miserable and their intentions were based on jealousy, bitterness and one-upmanship and I didn't want my children to have to experience that all the time.
If there is any chance of saving the relationship - do try - but don't let people make you feel bad. They are making you feel bad now, aren't they?
For many years I found that 'little contact, but we haven't really fallen out' worked well for the kids...they don't think there is a major problem and they can call on them, but none of you have to put up with it.
Final warning though - this worked until my kids got to their teens and my mother attempted to form friendships with them on Facebook which were based on undermining my parenting and slagging me off unfairly - hence the now complete banning...
My kids agree.
But do try if this people really care about you.