Hi Wild, Lots of problems, but I think a lot of these stem from his masturbating, I think when he has been masturbating its been done with a firm grip, now some of us men know a women can grip a mans penis, but not hold for the length of sexual intercourse, so he needs to retrain his hold when masturbating, this should get you over that hurdle.
The next thing is length of time. there is an exercise called edging, he or you can find all about this if you google pegym, just look under exercises, and away he goes.
The feeling of urination, tell him to go with it as he should find he will ejaculate.
He also needs to find other ways to ejaculate why masturbating, get him to stand up, legs together, legs apart, one leg up on a chair, you should work with him doing this, try having a masturbating weekend with him, but use lots of lubrication, and he should when masturbating, this would make it feel more like a vagina but at all times to use a featherlight touch, this mimics a vagina, the more he uses a featherlight touch, he may find then he can ejaculate inside you.
Hopefully the last hurdle, comes his erection time, get him to try jelqing, its a PE exercise, you can find this also on pegym, reason for doing this exercise, it will help get his blood flowing down his penis, but tell him to just keep it to gentle jelqing and no overdoing it.
I will send you some info that might help, its some herb stuff I take for ED, I'm not saying he has ED, but for good erections men need good clean blood, a lot of what I take is for this, and it works.
Do hope all this helps.
Good Luck
PS his accident some years ago, I had something the same. when I had a manhole break under me on a building site, things just went back to normal, was still having sex with them swollen, they were like that for a couple of weeks, all black and blue as well, bit of a shock to the wife, as she had to take picture as well.
He might want to see a urologist to check if there's damage after that trauma that's keeping him from maintaining an erection for long.
To try to train him to hold it longer, you can get him really close, and then back off on the stimulation for a bit until he's under control, and then continue. He has to know when he's about to *** for that to work. They also recommend kegels, where you do sets of clenching the muscles you use to stop peeing. He can start with 30 reps 3x per day. This may help him hold on longer, but if he's got a problem with the pipes, it might not do anything.
If anything, I would guess that not masturbating for a while would give him an even faster trigger, although it might make him *** inside you.