un-doing damage

Question
Hi, I am looking for the answers to a couple of questions.
I have 2 ferrets, both are males. One is 4 and one is 3years old.
I feel sick to my stomach because I know the conditions they have been dealing with is neglect. I am a Junior in high school, and I know that it is not an excuse, but they rarely get out of their cage!
It has been such a long stretch of time that they barely get out that both have developed aweful personalities.
One is partially bald from the stress. This same one, the older one is also extremely thin despite eating. I watch him eat, I know he does, but he will not gain weight. He has always been naturally small, especialy in comparison to the other very large ferret, but he is exceptionally thin now. It worries me greatly.
This thin one bites and scratches in the cage constantly. When I let him out now, he gnaws on everything in my room, which makes it difficult to want to let him out at all, but I know it is my own doing that this has happened.

I feel aweful for my ferrets. I want to attempt to make it better for them, how do I even attempt to un do the damage I've caused on them?! Is there hope in finding the well behaved, sweet, happy ferrets I once had?

If I fail at making their lives better, I do want to give them better owners who can care for them, but I am worried they won't get ones who will care about them if they are so nippy now... I at least know I will feed, water, and change their cage. But I fear if I do give them up, no decent people will want "bad" ferrets.

Neither of my ferrets have ever been to a vet over all the years I have had them, they only had whatever the pet shop gave them before I bought them.
I have not done this out of neglect, but merely lack of financial means. I am a teenager, and I am only  just getting a job. My parents never had the extra money to let me take either of my ferrets to a vet.
What should I do? If I save up some money, what should be my priority for them? Any shots? A basic check up? What?
I'm almost too afraid to know what the results of a basic check up for my older ferrets would be. He is overly thin, partially bald from stress, and his butt has has strange scabs for at least a year.
Can ferrets teeth grow too long? If that is so, I am nervous that has happened as well, that would explain why he gnaws on things constantly now... including a nice jab in my finger...

Please help me,
I want so desperately to right my wrongs and make the lives of my precious ferrets so much better.

Answer
Well let me first say that you must get them to a vet.  The thin and balding ferret probably has adrenal disease and requires vet care.  Both are (in most states) required by law to have a rabies vaccination and also require distemper shots.  Start there.  Ferrets are not cheap and their vet, an exotic vet, is more expensive than a regular dog vet but ask if they will work on a payment plan.  Really, don't wait until you have saved money, try to get them in now.