Im confused about one of the mechanics for the tiphereth realization

in the KOG phase where he spawns crystals and i need to destroy then,how does the game decide whoch librarian ges a crystal?

because i made that the one librarian (librarian A)who was gonna get 2 attacks destroy two crystal,i did that by making a faster librarian(librarian B)attack the crystal first to weaken then and the other one could kill them since they would he on low hp,but for some reason even though i saw librarian A destroy the TWO crystals,next scene he only had 1 crystal card while librarian B also had one ,which should be impossible since B dint destroy any crystals