Griffith's lists 7 Sinon's.Here they are with Barony, Parish, and Townland.
1.Sinon, Islands, Kilmaley, Sheehaun
2.Sinon, Jun., Islands, Kilmaley, Sheehaun
3.Sinon, Islands, Kilmaley, Letteragh
4.Sinon, Islands, Kilmaley, Letteragh
5.Sinon, Islands, Kilmaley, Booltiagh
6.Sinon, Inchquin, Dysert, Kilcurish
7.Sinon, Inchquin, Dysert, Ernagh More
So, Ray, it looks as if your Sinon could be in one of two parishes, Kilmaley or Dysert. We are probably looking for his father, as Griffith's lists only head of household.Unless your Sinon was on his own, we would be looking for the father.If you know any siblings of your Sinon, we could check where they might have been living, which parish, etc. That might help narrow your search. Also, if your Sinon died in the states, his father might just be listed on his death certificate.I have had great luck getting the parent names for ancestors who died after 1890 in the states. I have a source in NY for death certs, but do not know where you would be looking.
Another thought, two with the same "address" might be two different people, or the same person with two pieces of property.
Knockerry is in the Barony of Moyarta, Parish of Kilrush. This is not adjacent to Kilmaley or Dysert. Kilmaley is closer though.
Good luck, June