I always feel sorry for people not lucky enough to have a completely cohesive family.
James, it sounds like your older sister and you have a good relationship. Cherish that. Your middle sister sounds like she tries to be different to stand out and get attention. She sounds radically different from you and your older sister. The best thing you can do is acknowledge her shortcomings in your eyes and try to see things from her point of view to understand her and her motivations better.
As for her 50th, celebrate it like a family would, not like a group of college buddies would. If some in your family want to go along with rafting, let them do it. Make plans with your
sisters for some kind of gathering to celebrate in a more low key way that everyone can participate in and be comfortable. Sounds like all will have to compromise to get there.
I don't know you or your sisters so I can only go on what you post. I hope you eventually get to the point that you have a good relationship with all in your family.
