Are we eligible to seek sole custody, Texas?

Our daughter and us, the grandparents, have joint conservatorship over 2 children who have lived with us the majority of their lives. Their father is deceased and the mother was receiving the Soc Sec Survivorship benefits, our request to her would give them little amount which we would put into a college fund for them. After our research, Soc Sec changed the payee and we continue to input that amount in there. She has always been argumentive, violent, with an unbalanced mentality but changing the payee has made her treatment towards us worse. She has been jailed twice, one is for violence with a boyfriend. Somehow she managed to file a restraining order but he is now in her life again. We fear this violence will reoccur in the childrens presence and want to seek higher conservatorship with maybe supervised visits. The older boy states she cusses alot in their presence. The Legal Order states visitation will be on an agreed basis by all three and is not specific. She has been pic