Twilight check in is free for everyone on the VA flights from LGW.
DTD check in will be $10 per person unless you are VH, Flying Club Gold or Upper Class.
TBH with online check in now I would do that and not pay for DTD check in. Bell services will store all your bags for you and you can just collect them on the way to the airport. Just use the bag drop desks for which I have never seen a line.