When I was reading this post all I thought the entire time was that I had written it. 15 weeks ago I had an Arthroscopic hip surgery to remove my FAI or femoacetabular impingement. My results, with a ton of work on my own and with my pt, have been tremendous. I had the exact same issues. When I arrived at my pt a week after surgery I was so tight. My internal rotation was less than 0º now I’m close to 40º. I could barely keep my torso upright while squatting and now I’m able to keep a pretty vertical torso when back squatting and air squatting (overhead and front squats are still a work in progress). The surgery is vital in your situation. I was also born with naturally impinged hips, but my right side was greatly increases due to a prior hip surgery when I was 13 that caused the osteocyte to grow so much more than my left side. Surgery, in my opinion from what you wrote, is the best and pretty much only option. The results are pretty awesome. I no longer have pain when sitting for long periods and my overall movement has greatly improved. Good luck, my friend!