They might not stop in 1846 - many of the FindMyPast Welsh parish records are a wee bit muddled - I've found quite a few that have been mis-indexed. There's a thread about it on the Merionethshire board but it applies to other counties as well. Also, given that John P seems not to use his P initial until the 1901 census, he might well not have been baptised as anything other than John

However, from the census ref that I gave, we know that Mary Roberts parents are David Roberts and Margaret, which will take Alison back another generation. It might be worth doing the same with John Jones, plasterer.
Gadget