I know it isn't easy. I had huge student loans to repay when I graduated from college. I also had a family to support. But it's so worth it to get an education and a career that satisfies your soul.
It has been just over a year since my final payment on the student loan was made. I can't put in to words what a sense of accomplishment that was to truly earn my own education and pay for it all on my own. It made me appreciate the value of it that much more, particularly after hearing JWs taunting me that I was wasting my time going back to school because Armageddon Was Just Around The Corner™.
There may be scholarships or grants that do not have to be repaid to help your nephew financially. He may need to plan to have a lighter course load to allow him to earn some extra money to pay for books and tuition, and also take some summer courses to help lighten the course load even more. Have him check into getting second hand textbooks (same edition as his courses require) from students who may have dropped a course or no longer need the textbooks.
Can you help him out in some way? It doesn't have to be financial. It could be to have him over for meals regularly, to make sure he's getting enough to eat (because we all know the limited nutrional value of ramen noodles... ) or to get him some toiletries (shampoo, soap, deodorant, toothpaste, etc. because they get de-prioritized when cash flow is limited) or just to hang out with him and let him know that you aren't going to leave him in the lurch like his parents did. I used to buy a chicken on the day the supermarket marked down their meat by 50% to make room for the fresh stuff. I'd roast it on the first day and we'd have maybe half of it for dinner, and half would be leftovers. I'd make sandwiches and a casserole with half the leftovers, and I'd use the carcass to make a big pot chicken stock and put the remaining leftovers in soup, using some celery, onion and carrots and leftover pasta. I paid maybe $5 for the chicken and fed my family of 5 for almost a whole week. If your nephew is willing to learn some basic cooking skills, he can stretch his food budget a long way.
Could you offer him room and board without creating a bigger problem for him with his family? He may really appreciate that someone in his family wants to help him succeed in college, even if you're limited in the way you can make things a bit easier for him.