There is a book "Character certificates in the General Land Office of Texas : from the files of the General Land Office, Austin, Texas."Too bad your sister didn't know about that before she went to Austin.Or, did she make it to the General Land Office in Austin?Character certificates should be separate from land records.
The book was published by Genealogical Pub. Co., 1989, c1985, Baltimore, Md. I don't know if "all" of the certificates are kusted in that book.
As for marriage record that early in TX, they didn'thave marriage applications as we think of them today.Probably just an "entry" in marriage book.Unless one or both were underage, then parent or guardian would have to give consent for the marriage.
You're into a time period in TX when records are hard to come by.And, those that were generated often didn't survive time, either.(^_^)