Sorry, I committed the sin of assuming you had the 1901 census as you knew all the children's names.
Took a while to find them in 1891 as Ancestry's indexing has joined them to the Davies family next door but they're Thomas on the census itself.
20 & 22 Little Darkgate St, Aberystwyth RG12/4558 folio 68 pgs 35-36
Daniel Thomas head mar 36 draper & outfitter b. Llangeitho
Elizabeth E wife 35 b. Aberystwyth
Mary J dau 9 b. Aberystwyth
Edith S dau 8 b. Aberystwyth
Ebenezer R son 5 b. Aberystwyth
Elizabeth P dau 3 b. Aberystwyth
John Rees Jones nephew 21 joiner b. Llangeitho
John Bonsall 22 draper's assistant b. Aberystwyth
John Wm Jones 17 draper's apprentice b. Grantham, Lincolnshire
Samuel Thompson 16 draper's apprentice b. New York, USA, British subject
Elizabeth Williams 17 general servant b. Cards, Blaenpennal
Margaret Davies 15 house servant b. Cards, Cwmystwyth
Think you'll need a birth certificate to get Elizabeth's maiden name before you can find their marriage. There's nothing showing on FreeBmd that looks obvious.
Edith Sarah Thomas june qtr Aberystwyth vol 11b pg 66
Luckily, Ebenezer's middle initial is on the census as there is more than one Ebenezer Thomas registered in 1885
Ebenezer Rees Thomas june qtr 1885 Aberystwyth
Middle name makes Daniel's father in 1861 look good.
Can't see Daniel in 1871, but he should be apprenticed and could be anywhere.
If you having problems with Welsh place names, you could post on Rootschat and ask. This is a list of Cardiganshire place names that might help
http://www.genuki.org.uk/big/wal/CGN/Gazetteer.htmlIf he became mayor, he must have been a local councillor. You could ask the local archives for some help
http://archifdy-ceredigion.org.uk/I'd suggest visiting the archives, but your profile doesn't say where you are.