NYCNUT
If you try the site Mayo.ie and follow link for what's on, at he National Museum near Turlough,Castlebar Co Mayo an event this Sunday,they also hold monthly Geneology meetings.You may get someone who could look to see if they have any information to help.I have visited the museum when first opened.I see you have Peter's death notice in 1918,do you have a copy of the death cert as sometimes Clinton records show name of Townland they came from not just County of birth also full names of parents.
PS the marriage cert on your tree states Peter William not Peter Joseph as you say.