Is it legal for a 17-year-old to date a 20-year-old and move in with him and his parents and not get anyone into trouble in the state of Texas?

It's legal for you to date him, provided that your parents don't object to it. If you move in with him/his parents without permission from your parents, then under Texas law, they could be charged with: HARBORING RUNAWAY CHILD: A person commits an offense if he knowingly harbors a child who is younger than 18 years and is voluntarily absent from the child's home without the consent of the child's parent or guardian for a substantial length of time or without the intent to return. INTERFERENCE WITH RIGHTS OF GUARDIAN OF THE PERSON: A person commits an offense if the person takes, retains, or conceals a ward when the person knows that the person's taking, retention, or concealment interferes with a possessory right (the right of a guardian of the person to have physical possession of a ward and to establish the ward's legal domicile) with respect to the ward. ENTICING A CHILD: A person commits an offense if, with the intent to interfere with the lawful custody of a child younger than 18 years, he knowingly entices, persuades, or takes the child from the custody of the parent or guardian. And possibly other charges as well.