Do you have the birth certificate for William to check the address? His birth was registered sept qtr 1861 Cardiff vol 11a pg 250. They could be at the same address for the census.
Just wondering about this burial - transcription is Ancestry's but the image looks like it could be LewisBarbara LewinAge: 37Burial 2 Mar 1867, Stapleton, Holy Trinity, BristolAbode is General Hospital, Bristol