Car Loans

What is are the laws regarding minors and car loans?
My younger brother is 17. He wants a car and neither his mom or my dad will co-sign for him. My husband and I told him we would, but my brother’s mom told him that he can’t legally get a loan without her concent. I used to work at a bank and I know that minors cannot open a bank account without an adult, but the adult does not have to be the minor’s parent.
I have been searching the internet for the law in Illinois regarding this issue, and I can’t find anything. Can someone help?
Since he is a minor, he cannot enter into any kind of binding contracts until he is 18. There is nothing that states that the adult co-signing a loan for a minor HAS to be a parent or guardian. The only thing is, if he defaults on the loan you will then be responsible for the loan (but since you used to work @ a bank, you should already be aware of what you are getting yourself into if he defaults on the loan).
If you haven’t considered this yet- he’s going to be in the same position when he goes to get insurance & his tags for the car. Can’t due to being a minor.
Good luck.