1881 Census (RG11 5584 42 5)
1 Pistill Du, Jane Roberts, Head, Unm, 73, formerly domestic servant, born Caerhun
" Pistill Du, Robert Roberts, Brother, Unm, 65, Agri Labourer, born Caerhun
2 Pistill Du, Jane Owens, Head, Widow, 72, No occupation, born Caerhun
3 Pistill Du, David Roberts, Head, 79, Annuitant, born Llanrwst, Denbighshire
On the 1911 Census, John Roberts' PoB is transcribed as "Llansant". The original entry has been crossed out (Caernarvonshire Caerhun) and replaced with "LLan____ ?" - which could well read Llanrwst if you wanted to. Unfortunately, the County was not included.