I'm no skills autist, but I'm certain skills, at least those of the same "slot" don't stack.
Kind of like specials with two attack up passives, it would take the one which has a higher value (after the fix of first or second position)
Though the description is variable to who is based on students of x value, in this case armor type over red winter students.
You could have Cheringles, Shigure, Marina (ugly alt) and Canoe as strikers, another RW special and any cost up special like Shiroko or Himari.

I can only imagine how much skill gain there would be. It may even be faster to swap out one of the RW students for Seia and her EX cost boost on top of the others.
This is too much thinking for 10pm.