Family of six, no small children looking for travel options from Dublin to London this summer, June.
Unless you’re considering a boat from Ireland to England, then making your way to London over land, fly. Do you have frequent flyer points to use with a particular airline? If not, see what airline flys the best schedule, at the best price for you.
Note that some airlines will fly to Heathrow or Gatwick airport. Others may have lower prices, but will fly you in to one of London’s other airports - like Stansted or City, which would mean a more complicated effort to get into downtown London than if you flew into Heathrow or Gatwick.
Fly….cheapest and quickest about 4 hrs. Flights go to all London airports, Heathrow, Gatwick etc. Ryanair and Easyjet are cheapest.
Ferry+train - depending in where ferry lands in UK. 8 to 13 hours. Irish Sea is noted for rough seas!
Explore options here, then book with the actual carrier(s). I'd fly.