When it comes to families I believe there has to be a linchpin. Usually this is the mother, but failing that, it falls on anyone who cares to take it on. Everyone else in the family will gravitate to that person and possibly expect them to organise family matters. The rest of the family then choose whether they join in or not. When it comes to in-laws, their selfishnesh is all the more apparent because they can only be part of the family by joining in. If you value family life then keep it together. Those who don't join in sometimes will when they wake up to the alternative.