Hi ZZZ999
I've been living in Griffin Rath for the last 2 years and love it. You're right in saying that there aren't many large open spaces, although there is a decent size green in Griffin Rath Hall (turn right when you get into the estate). Not sure how large your dogs are, but it is a decent size space, lots of people play football etc there so it might be ok for a quick run around in the evenings
Otherwise the canal is fine for a walk as others have said, or if you fancy a longer walk there are some lovely walks down in Carton estate, of various lengths.
The dormers are really lovely, nice size and layour and good space to the front and back. Hope it all works out for you