Please help aunt wants custody

So here's the facts my son and his mom moved out of my house in Texas to live with her brother and his wife a few years ago we had no child support or anything in court I did sign the birth certificate. Well earlier this year my son's mom was kicked out and my son stayed because of school and friends and we aren't financially able now the aunt and uncle want us sign custody of my son to them so he can be enrolled in school. I said no but I'll do a guardianship or a pcm. The school said that's nit good enough tk enroll him the aunt and uncle claim the guardianship is worthless. What can they like to get fully custody? I think they want to adopt hom for financial reasons.