My personal opinion on who should get my seat is the elderly woman, because as she is old if she happened to fall over then she is more vunrable then the other people, as she could cause significant pain in her back. This is because even though the man with crutches has an injury he is able to be fixed if he hurts himself. Despite all this you could ask the other people to give up their seats to give to the other people (who need it more) and give them the chance to sit down. If the old lady sat down in the seat, you could stand near her to help her if she needs anything, and help her if she needs any help when she stands up, or when she needs to get of for her stop and just make sure she goes of at the right time. If the old lady got of before you, you could then make sure that you would give the seat to one of the other people.