I don't practice in TX, but yes. You can get a restraining order through the county court civil department or if there is already a TRO you can request that it be extended to include you.
Edward J. Blum
You can file a complaint by calling 311 (for non-emergencies) or 911 (for emergencies). They will take a complaint from you regarding the harassment allegations, but your daughter will likely have to talk to them herself to file any assault charges.
The local district and county attorneys may be willing to represent your daughter in getting a protective order against her ex-husband, but again, since she is the victim, she is going to have to take an active role in this process. She or you can get a PO covering your grandchildren.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.