Question About Guardianship Of Minor- Complicated Situation.

Hello, I have a little issue with my friends son and need advice if anyone can help. Heres some background..

I have known hin since he was 4. I have known my friend since we were in middle school, became friends when our kids were in preschool together. Her son is now 17, his birthday is in October and he will be 18. He is staying with us now (him and my kids are best friends). His dad has legal custody of him. He gets the support payments from mom. He gets the state benefits for the kid and all that. But he has been living with his mom for the last 3 years, because that's where he wanted to be. and dad doesn't seem to care because he's getting paid.. so why would he lol Now, he's been living with us full-time for a month. Has been at our house every weekend for the last 6 months.. stays longer if he can. His mom and her boyfriend recently got into an argument with him and thats why he left. The mom cares about him, but doesnt seem worried since he's at my house. We haven't talked. She's been mad at me since autumn 2024. She's very childish. But she knows he's taken care of here.

The issue is... the kid needs to see a doctor. He needs to go to the dentist. I'm not worried about money, because he has a job. He can pretty much get whatever he needs. But he needs a gaurdian or parent when he goes to the doctor. They said they won't see him without one. So, what can I do? Should I talk to the dad about taking over as gaurdian? Can I? I mean, October is still as while away and it's going to feel like forever.. Especially since he can't do anything without a legal guardian or parents permission.. Any advice on what steps I can take will be appreciated. I am just trying to help him. I am looking at his interest here. I am not trying to step on his parents rights or anything. Neither of them seem to want to communicate with him or me.. Other than his former step-dad. He's the only one who came and got him yesterday. But he has no rights in this, or I'd be consulting with him lol

Thank you for any help you can give me