The elbow is complex. Like you mentioned, there is rotation of the forearm and shoulder that happens when you extend or flex your arms.
The triceps( 3 heads) biceps( 2 heads) forearms( brachialis? Forearm"flexors"?) and a bunch of stuff I don't even know about all have to work together to get it right.
Sometimes your exercise selection over uses some muscles, and under uses other muscles. Over time, this leads to imbalances, which cause the joint to move incorrectly, which makes the imbalance worse. The overuse/improper use and joint moving wrong eventually cause inflammation and pain. You've heard of "the lazy head of the triceps" or "golfer's elbow." Overuse and underuse issues!
You have to retrain your elbows to work right.
For the triceps, try band Pushdowns for high reps(100+). Just like Louie Simmons says.Think about doing some with your elbows "in" some with your elbows "out" and some with your arms over your head. The bands are good because you can change the angle of your wrists and elbows to make the extensions pain free. If it hurts, don't do it, that's the overused muscle/movement pattern. If it feels good, do it. That's using the under developed muscles.
Weird stuff can happen with your biceps too. Sometimes the brachialis and forearms muscles start pulling harder than the biceps. If this is the case alternating dumbbell curls with a twist, that really hit the bicep Will feel great. Reverse curls, that hit the forearms will feel like torture. So find what doesn't hurt, and do that to retrain The way your arm "flexes."
Don't get discouraged! Even if you can't bend your arms you can do;
-Fly motions for chest
-Delt raises for shoulders
-Shugs standing, leaning forward, chest supported, or laying face down.
-Straight arm pull downs on a cable for lats.
Also, don't neglect your shoulders. I like this.