Last minute Deal from UK or Ireland.

My family of 2 adults and 2 children. We are looking at a last minute deal the last week of August and we cant decide if we should go from Dublin or Manchester, we need to go over there just before hand to reknew a passport so should we just Fly from there or come back and fly from here?

manchester has many cheap flights but with the strength of the euro it might work out as the same price....

is it necessary to actually go to manchester to do passport? cant it be done thru british embassy in dublin?