What can I do I feel helpless? ?

So i just bought a 3 year old quarter horse / paint gelding. He's only about 14.1. I'll start with his story, so there is this girl she's about 25 and she had a baby, right after her mare had this foal, so she gave him to her cousin to take care of and to train, her cousin is 13, and has only been with horses for a year, has no idea how to train a horse.. So he was just sitting in the field at her cousins house(25 year old) who did I mention has no running water or hydro? So anyways she started working with the horse but then she got pregnant again. So clearly this baby horse has been sitting in his field, sorry his 20 ft x 20 ft hole with NO grass and he is up to his knees in mud. He's never seen another horse except his mother, who died when he was about 1 and a half. So the girl that owned him before she gave him to her cousin, was convincing me not to buy him and she said she was going to work with him . The thing is she has no idea how to train a horse. She thinks he has aggression problems that she can fix, but clearly when he throws and ru s his head on her it's not Aggression he just wants some love! The poor guy , I feel so bad. So I was supposto rent the trade from the girl now the lights are mysteriously " broken " and I can't use it , so we found another trailer, but like I know this horse is going to a great home, where he will be fed proper hay and actually grain. How do I introduce him to other horses? And where do I start my training to get rid of bad habits?