When I mentioned turning off the colliders, it's just dynamite, not the player, which is a simpler solution than working with the separate layers.
The time of the box collider of the dynamite off, is only to avoid that it collides with the player in the launch.
Player colliders remain normal. But that could cause the dynamites to grab the walls. So it's a temporary solution.
On the dynamites, I believe that only 1 in the match, is enough, COD MW1 only uses 1 also, depending on the amount of players in the match, each 1 with 3 dynamites, the game gets many explosions, which disrupts a little "pollution sound ".
How many people are creating the game?
What solution are you using for online, is Photon?
I intend to study more multiplayer in the future and I really enjoyed the performance in your game.