There is a possibility that the R. S. Mobley you mention is Richard Smith Mobley, son of Richard H. Mobley.But, I don't know for sure.Since Martha is there in Bell county it does seem likely that R. S. Mobley and Richard Smith Mobley are the same.
Richard H. Mobley and Martha White's children were:
Rachall, Mary Elizabeth (my ancestor), Martha, William, Richard Smith, John, and another son John.There also seems to have been a sister Susan (at least she was living with the family in the 1870 census.
If R. S. Mobley and Richard Smith Mobley are the same, then he ended up in Holdenville, Oklahoma.
This Martha Ann Mobley could easily be Martha White's daughter Martha.I am in contact with someone else about Martha Mobley and need to find out if there Martha was ever in Texas, so far as they know.
I don't know if I answered your question or not, but if this is useful please contact me.