Once you "combine" the luv vouchers, they become travel funds, travel funds can only be reserved in the original passenger. So the plan that you have listed above would only cover your travel and not anyone else's. Regarding the check in, you could purchase early bird, or using 2 vouchers and CC per person (assuming the flight is more than vouchers) you would reduce the amount of vouchers to 3 check in's then booking 4 people on 1 reservation reduce the amount of check ins.