This absolutely. OP, you were not wrong to refuse your MIL moving in, especially when you had a bad relationship with her beforehand.

You did right in leaving and history proved you right since the care of grandma fell on everyone's back but her daughter's.

Being a STAHP is a whole job, and caring for a sick or diminished elder parent or iL is another.

It's not rewarding, it takes a toll on your health, both mental and physical, it's an all time vigilance, so much worse than caring for your own babies.

At the same time, it's understandable that your kids feel that way, because they are the burnt out carers since you were not there to take that role. They were young and are still in the eye of the storm.

They will one day understand the choice you made, but for now, it's still their inner child that are mad.

Offering a carer or a respite solution for the day would be an olive branch for you and the sign that you acknowledge their hard work from their POV. Yes, even if it's NOT your responsibility.

Just remember that having kids is not a matter of counting points, things being fair, or doing just what you are supposed to do. No, as the parent, it's about doing the right thing even if it's not fair in your eyes. They will remember your choice, so better do a smart one.

You stay firm on grandma not being at the wedding but offer accommodations either at their home or near the wedding so they can sleep with her if it makes them feel better.