Hi,
Johanna57 - to be honest there sounds like an awful lot of ' he said / she said' in the family.
If you really want to trace your family back further and correctly you will need to start investing in some paperwork.
The certs are only 4 euro each from the GRO.
Once you have Thomas' marriage cert in front of you, then you can proceed on.
If you let us know who Thomas married and roughly when, we can get you the details you will need to order the marriage cert.
Best Of Luck
Tara