For your friend with the hip, he has a CAM hip. Look for that, Kelly talks about tha in some of his videos about internal rotation (he is talking about mushrooms when talking abou it i think 😉 ) = hip impingment !!.

He really need to work with distraction!!!! always, try to get as much of mobility as you can and work on evrything around it like David was saying. Definatly work on glutes  and posterior capsule of the hip !!!!

Work on i but be gentle , listen to the body, cuz his cam is here and he can dameg his capsule/labrum when he overdoes!!!!

Greetings from belgium