As for the shot conflict, there are a few methods for handling this.
What you'll want to do is to have a large location for each player
to encompass the maximum firing range of a dark swarm (18x18 grid
squares, if I remember correctly), and then to activate the "Firing
Event" only for the player who has the dark swarm inside their
location. Alternatively, you could center just a single encompassing
location on any dark swarms in the Anywhere location, and check
which players are within that location, then activate the shot for
that player(s).

The problem now is when shots occur close to other players, as there
won't be any way to distinguish between which player cast the dark
swarm. One solution is to simply disable dark swarms cast next to
more than one players altogether, as I've done in my Trigger Happy
D map. However, as you may have noted from playing the map, this can
get frusterating when players are ignorant of this rule, or else in
a hurry to make a shot.
Another solution is to register the shot for the first player whose
triggers catch the dark swarm, which could be problematic for one
player shooting into another's zone and having all the shots register
for that player.
Another solution still would be to register the shot for both players,
which can still be problematic but it will at least guarantee that
whoever makes the shot actually gets it.
Finally, you could avoid the situation altogether by preventing
players from getting close enough to fire within their zones, either
by physically preventing them from with terrain blockers, barriers,
or boundary locations, or else relocating the players to their starting
positions if detected within each others' zones (or else relocate only
if shots are detected in their shared zones, maybe after a certain
limit, so players who abuse the no-shot rule frequently will be
moved before those who don't.)