Grandparents have limited rights in Texas. I have put a link, below, with more detail. In general, if you want to obtain custody of your grandchildren you will have to establish 'standing' first. This is the right to even ask for custody, and is difficult to obtain. The most common reasons are the parents voluntarily giving up custody of your grandkids to you, or the really, really bad situation the grandkids are in with their parents. Just seeking some possession for yourselves is difficult. You would have to prove that the lack of access to your grandkids would significantly impair them. That is a high standard, and probably requires a mental health professional to back you up.
Grandparent rights are one of those areas of the law with a large amount of misinformation surrounding it. Make sure you find out the truth before proceeding. Here is that link:
This information is not legal advice and does not form an attorney-client relationship.