the inheritance? Perhaps this is because of their low character (refusing to help) yet very interested in the money. They have very strong feelings about not helping/visiting with their aging parents, yet paradoxically, they have very strong feelings about the inheritance. I've read posts that sibling(s) are never around to help; trust me they will be back when there is money involved.
If the siblings are helping with the senior parents and sharing responsibilities, it's a a great thing and I would consider myself blessed. I'm not sure if the thought just doesn't enter their mind or if it enters their mind and they push it out. lol Either way, I don't count on it. If it happens fine, but, I've learned to just depend on myself and I then handle it, delegate it to a responsible person or pay to have it done. No waiting on others. lol
I will say that adult kids shouldn't have to revolve their lives around the care of an ailing senior parent. That's not fair, nor do I expect that, but an occasional thing would nice.