if someone ELSE caused the problem, that someone else should make it right. When my daughter was hit by a car (also by an elderly person) and dragged 25 feet, her insurance company didn’t want to pay for her medical bills etc because “we had insurance.” Well no kidding, but we wouldn’t need to USE our insurance if YOUR customer had paid attention and not hit her. The police were like, yeah, it’s obviously the victim’s (my daughter’s) fault for crossing in the crosswalk.
Insurance companies don’t pay out unless they’re forced to. It sounds like it is going to be a long convalescence with a lot more outlay than your BIL/SIL might have. It sounds like they need to find a lawyer and start proceedings. It’s one thing to file a frivolous lawsuit and another to have to because the offending party/insurance won’t take care of things.