We flew with Vueling at Easter. We checked in large 1 bag and they weighed our hand luggage (from Cardiff). Luckily it was just under 10kg!

Flying back from Barcelona they didn't weigh our hand luggage but saying that, we didn't go to the bag drop counter as we left our checked bag here at the house.

I would suggest your friends avoid the check-in area and go straight through security (providing they have printed their boarding passes).