My father-in-law was married in 2019 and in 2022 his adult step daughter filed a power of attorney in the state of Texas over her mother. Any advice?

One does not file a power of attorney over someone else. The person, called the principal, signs a document that states who will have power over their affairs, when they will have them, and what powers they may have. The principal must be competent when they sign the POA document. If the POA is durable, it means that the principal is granting the powers to the agent now. If the POA is springing, the agent only acquires the powers when an event occurs, usually when the principal becomes incompetent. Is the mother now deemed incompetent? Was there a reason your father-in-law's wife didn't name him as her POA agent? Whose name is on the title to the house? If you think the step daughter is not acting in her mother's best interests, you can bring the issue to court. Not fun. Not cheap. But you can do it.

So... Your husband's father married a lady in 2019. The lady's daughter has, perhaps, a springing DPOA? which in 2022 she used to have her mother admitted to a nursing home.

Your FIL was living in the lady's, now his wife's, house. After she was admitted he then became homeless. How, exactly? What happened?

Did/does the daughter question the validity of the marriage?

Where is your FIL living now?

Your profile has more info:

"I am the step daughter in-law my father-in-law has been duped out of his living arrangements his wife taken to a nursing home by an adult daughter with power of attorney his household and he's homeless and she is basically being kept away from him as a spouse my question is does him being her spouse supersede a power of attorney filed after their marriage by her adult daughter "

She can't "file" POA -- that's not a thing if she doesn't have a power of attorney document.

Was this a document from before her mom married your dad? Did your stepmother and dad update their docs after they married? If not, t.comen it might be valid. If her mom is competent, she can simply write a new POA giving it to whomever she wants,tand that renders the old one invalid. If she isn't competent, then you've got a problem. Your dad might have to see an elder attorney to find out his rights as her spouse.

More info needed…