I'm your dad's cousin Molly Woods's son Jonathan and I think I may have tracked down your Jarvis great-grandfather. I've found a Thomas Jarvis on the 1911 Census who is working as an attendant at Graylingwell Hospital in Chichester but he's not Irish. I've added him to my family tree as your father's father and I've added some potential detail on him from the 1891 and 1911 Census, a Kent birth certificate, a record of him returning from Canada in 1949 and a Kent death certificate from 1961. I think it's probably the right chap. Hope that's useful.