Hello Janet,
There are several Forrest families in Blarney who have been there for several generations and I think that they are all related. Denis and John are family names so chances are that these might be the family you are looking for.
I don't know how many of them are left there as I left Blarney a long time ago but there were three farming families on the outskirts of Blarney, the postoffice used to be run by a Mrs O'Leary who was originally Forrest and there is a hotel in the village called "Blarney Castle Hotel" which is owned by John (johnny) Forrest.
Why don't you send them an email to see if they can help.