Many thanks for all this information, it's invaluable. My great grandfather was the David Nelson (think that was the Daniel Nelson at the bottom), as all the others fit. Could you please tell me how I now find the reference numbers to apply for the birth/marriage certs?
Also, is there any way of seeing the census records to see what the address was? I found on the 1861 census that David and Thomas (12 and 14yrs old) were resident on Anglesey, so would be interested to see who else was there, and build a picture that way.