What is the Statue of limitation on statutory rape in texas.....Texas law please criminal law it wouldnt let me scowl down sorry

My firend started to date a 22 y/o when she was only 12 they became sexully involved she ended up having 2 kids by him anx married him at 18. Well she left him about 4 years ago well he try to fight for full custody well of course loss cause he couldnt pass a drug test and of course no jugde is gonna take away custody from a mother without good reason. He keeps calling a CPS and the cops on her of corse they dnt find any thing. But he is adamit about getting full custody of there girls Her oldest is about to be 10y/o soon just a few years younger from what my friend was at the time they became sexually involved and tht scares her.she has custodyof the kids but is afried tht when he gets cleaned up they might grant joint custody is there anything she could do to prevent that cause of his past history with her being a child at the time. My friend was molested by a few men when she was younger so when he came along she figure he could protect her but fail to reilze he was doing the same.