1. Ditto, I also think that looks like Low Ringbone
Although when my TWH foundered and had torn ligaments he looked like that until I got him healed. If the horse did have torn or strained ligaments and nobody helped him, that might be the end result.
At any rate, those ankles have a question mark on them
2. Ditto, I am pretty sure he really needs to see a chiropractor, looking at his back
I can understand him being high-hipped as that is a genetic trait of some blood lines but, enough weight has been put on him that I think he is too high hipped for 16 years old and also that "hunters bump" is not at all normal.
I'd say he has sacrum issues.
3. I'd like to see clear pictures of the backs of his front fetlocks, if that is possible. Tape the fetlock hair to the leg, if you have to.
4. It could be the camera angle but, when I lay a ruler across my monitor, his knees are not even, indicating one shoulder might be higher than the other one. He seems to splay out on the right side only or he could have just decided not to square up for the camera.
5. Keep him barefoot until you find can get your own vet out to look at those legs.
I like his big ole Walkin' Horse head and he's a pretty fella
I think he's either been put thru the ringer at some point, or he's had a bad accident and his owners either couldn't or didn't want to deal with what might be long term expenses to keep him healthy (that doesn't necessarily mean sound).
Get your vet to look at him as soon as possible. If you can afford ultrasounds on those legs, get them. I would go so far as to x-ray the front hooves to see if there's any coffin bone rotation. Also, the top of the back can be ultrasound - it is very difficult to do with a portable machine but is possible if the horse can stand quiet long enough for someone to hold the machine over him and somebody else does the alignment and button punching.
Let us know what you find out