The thing that would concern me about making sure the cousins are aware of each other, as OP said she did, is that it is forcing it on them and almost like rubbing it in their faces that these people exist who are meant to mean something to them and they are missing out. That's different to casual references to the people. I wouldn't be on board with my MIL pushing cousins we have nothing to do with on my children, especially when so young. The kids probably don't know what to do with that information.
Adult kids staying and not contributing.
if your recycling or rubbish collections days are Monday,Tuesday,Wednesday
A quote for those blessed with a spouse:
Father's Day Sunday — nobody makes cards for this type of dad
In the end the children suffer. 
