Adults respect each other as equals

However even that isn't really the case here - you and DH are in charge of your family.

If you allow manipulation, that, perhaps, will continue into the next generation. Be a role model for your kids. Let them see that "guilt" isn't acceptable.

I would just remind them that the kids have busy schedules now that school has started just as they too have busy schedules with their travel and such. Remind them that you aren't moving anywhere and as soon as schedules align they can have a fun time with the kids.

So it sounds like they are trying to be emotionally manipulative? Doesn't sound healthy to me.