I think family arguments - especially with parents/in-laws - have a unique way of getting to us that arguments with other people (mates, colleagues, neighbours... even complete strangers) generally can't come close to. I've been involved in more than my fair share over the years, and I know that they've needled me for a good while afterwards. I think the best thing to do is to try and be pragmatic: can you all get past this? This is the preferred option, but if it's going to be the sort of thing people really can't move on from, then I think it's better to not see people than to see them and there to be resentment, more arguments, and so on. No point in everyone meeting up and being miserable - especially as kids come into the equation, too, and will be affected by their parents and grandparents not getting on.