Flexibility is the key...I was able to book saver trips for 9 family members to and from Santorini in the summer of 2015. Going over 4 of us flew BOS-MUC-ATH, 3 of us JFK-VIE-ATH, and 3 of us EWR-GVA-ATH, with flights on UA, LH, and A-3. Coming home, we all managed to fly on the same AC flight to YUL, and then split with some of us continuing to BOS and the rest to EWR on UA.
We also booked a couple of less than ideal itineraries for some of us, watched like a hawk, and changed to better ones when they became available. We all managed to arrive in ATH within an hour and 15 minutes of each other.