I am being deliberately vague about the details.
DH and I have plans with my family in mid December (Plan A). DH has now made arrangements with a friend of his (Plan B) which clash. Its not a total clash, but its highly likely that Plan A will be impacted in some way by Plan B. I have asked DH to find another date to see his friend and he said he would try.
But if he can't find another date, and my family plans end up being impacted, am I within my rights to decline to attend an arrangement with his family, the following week?