Sorry for your loss.
This will be a tough situation to deal with, and most likely someone will be disappointed. Before involving all the lawyers, it might make sense for someone to sit down with Mom and help her articulate what she wants. From what you have posted so far, she seems too struggle with that. That's not uncommon, and she may never be able to fully reconcile her views on disposing her estate and helping her children. What matters, though, is not what the siblings want. First and foremost is her welfare - she needs an advocate who takes her side and helps her make sure that her needs are taken care of without regard to the children.