Yeah but I will say as someone with eight aunts and uncles on one side: if DIL really is organizing events for her *entire* extended family, then inviting husband's mother and sister along will not even make a dent. Random people show up to our family Christmases all the time. My uncle's ex-girlfriend's old neighbor's adult kids sometimes show. If DIL isn't inviting them, she either has no reason to think they'd want to come, or she has other reason to not want them to come. Or these are not actually gatherings of all eight aunts and uncles and their entire families, it's "my two favorite cousins are coming for a long weekend" and MIL is mad she's not getting equal time to all several dozen of SIL's relatives put together. (Given the "have to ask DIL's permission to visit", I do suspect it's one of the last two, though.)