Custody laws for Florida and Texas????????

Samantha • TTC my rainbow baby. Lost my Zackery 3 years ago. Infertility problems, hoping GLOW helps.

I am asking this for a friend. It is not TTC related, but I don't know who else I can ask and I was hoping that some of you may be able to help.

A woman has had full custody over her 12 year old daughter in Florida, the father lives on Texas and has no custody, but the mother allows daughter to stay with him over the summer..... This year however, he mother agreed to let her daughter stay in Texas for an entire year with her father and sign a notarized agreement that after 1year time the daughter is to go back to her mother (done outside if court and mother has full custody)

Well now the father switched to claim his daughters social security in Texas (instead of Florida without mothers consent), and just sent mother paperwork filing for full custody.

???? Is he able to do this? What is he likelihood of him being granted this? Also in what state would the decision be made? Florida or Texas?

I hope someone out there has insight to this.