Legal Question in Family Law in Texas

If your mom has been living the house, you are both wrong. Your mother has a probate homestead which gives her the live in the house and have control over the household.

As Mr. Engelke said, you're both wrong. Wrong about the entire concept of all of this, I think. I'm not entirely sure just what you're talking about, but unless your mother has some kind of physical or mental problems which make her truly unable to conduct her own affairs (in which case you need to go to the probate court to ask for a guardianship), your mother is not somehow now under either your thumb or your sister's just because your dad passed away. Neither you nor your sister and her son nor anyone else has the right to move into what is for now your mother's house alone and either live there or start telling her how to do things.

If your father left a wil, the will needs to be probated, and if he didn't, the default provisions set out in the Texas Probate code apply as to how things are going to work. I could be wrong here, but something about your post makes me think that perhaps your family is from another country with very different laws. If so, please realize those laws don't apply to property and persons here--while you're in Texas, Texas law applies. Texas law provides that unless your ather left a will that says otherwise, all of his children will ultimately share equally in his estate, but for now, at least as far as the marital homestead is concerned, that belongs to your mother and your mother alone.