If there is 2 ninjas with "40 chakra move" then the character you placed on the battle field LAST will activate first.

If one ninja uses a 20 chakra move, the other a 40. Then the 40 chakra move will activate, this also means if sage naruto is in spot 1, and gaara(80chakra) is in spot 2. Then Gaara will go first if you have 80chakra.

If both ninjas have a 20 chakra move, say Iruka/Regular gaara. Then iruka will wait 1 character move, to use a interupt first.