I think you’re right to keep the siblings involved as much as possible. But I have a question: What’s your agenda? To get them to help or to get them to visit with their mother more often? These are two very different agendas. The helping agenda could lead to frustration—they are in-laws, which is tricky. Also they just don’t seem like responsible adults to me. But your mother-in-law doesn’t have many days left. So encourage the siblings to visit your home (after she moves in with you). Hosting family meals or gatherings is a way of honoring your mother-in-law and letting her enjoy her children. Maybe just leave it at that, if you can stand it.