Our family (2 parents, two teenagers) will be in London in late June, staying at the Marriott County Hall. Our flight to Dublin via bmi departs at 0810.

I'm looking for advice on the best & quickest (maybe low stress?) way to get to LHR Term 1 that morning? What time should we leave the hotel and what would be the best means of transportation at that hour? It is a weekday (Tues) departure. Right now we are all planning to each have one piece of carry-on size luggage and maybe a backpack. Thanks.