Everything here assumes laundry at your mother's house and a Boots run on arrival. That's what keeps this to one small case and leaves the rest of the allowance for the kids.
The bulkiest things you own, carried for free.
Keep these out of the checked bag. If it goes missing, you've lost the only reason you stopped.
Four days' worth, washed twice. Fourteen days changes the laundry rhythm, not the pile.
Two weeks is long enough that one soaking shouldn't strand you.
One set. Technical fabric washes in a sink and dries overnight, so it covers a run every few days for the whole trip.
All of it is at your mother's house already, or £3 down the road. This is the single biggest space saving on the list.