My father was adopted in the state of Texas, his records are sealed and I want to open them how can I do that if he is passed on?

Petition the court that has jurisdiction. They will want a good reason and a lot won't accept "curiosity" as a good reason. For instance, if you suspect genetic disorders that pass generations...

Usually the ONLY reason for opening sealed records is a medical necessity.

Technically, they're not YOUR records, and you have almost no rights to them.

You'd have to get a lawyer and fight to have them opened, and even then, the likelihood is that you'll only get non-identifying information, like medical records.