It’s really interesting to me that you have provided this additional clue because ankylosing spondylitis was literally the first thing that popped into my head reading your story. I agree with others that your story sounds much more than typical aging symptoms and you should seek the opinion of another physician.
Even if it ends up NOT being ankylosing spondylitis exactly - you should know that there are some hereditary factors that predispose to AS but also to other, similar conditions which are collectively called “inflammatory spondyloarthropathies.” Given your brother’s diagnosis you probably have a higher chance of one of these conditions because of your shared genetics. So yeah absolutely ask another physician until someone investigates your symptoms!