When adding a multiple-leg trip to Leon from a section SCHEDULE > TABLE you don't have to add the same crew members by clicking one leg by one and selecting crew in a right-hand filter (tab CREW).
Right now Leon will automatically copy crew inserted to the 1st leg also to the other legs of the trip, as long as the trip is on the same aircraft type.
On the attached screenshot you can see that all crew members were added only to the first leg. The the other 3 legs were added and once the trip was saved Leon displayed the same crew for all 3 legs.
This option also works if you add a single leg with crew, save it and then after some time add more legs to that trip - Leon would also copy crew from the 1st leg to the other ones.