I have a few basic "create 1 unit" triggers but instead, it creates two units for ALL of my triggers that are set to create one.. This is the first time this has happened. What could I have done wrong/How do I fix it?

If the triggers are under something like "Force 1" and there's 2 players under force 1, it will run 2 times, one time for one player and another time for the other player.

Is there more than one player running the trigger?

Yeah, it's for Force 1, Force 2, and player 8.
Create 1 battlecruiser for player 4. So should I set this trigger for Player 1 2 3 ect, instead of Force?

If several players running the trigger fulfil the condition, they will all do the action once each. What is the condition?

Use P1,2,3,4 etc. and use "Current Player"

Okay but, in the same trigger I'm trying to have them all have a switch set while at the same time the cruiser for player 4 is made. So I'm guessing the only way is to have these two actions in separate triggers?

Correct.

Actually not.
The better solution would be to use a death counter set to 1 instead of a switch and then check for
All Players have suffered at least [# of players] deaths of 'switch dc'

uhh... at least if you're trying to do what I think. If that doesn't work you'd have to tell us more about the switch's usage and purpose.
In any case a switch is a global variable. If a player sets it then it's set for everyone. Death counters is a Current Player variable (every player has its own count) so you can check how many players have it set to 1 (or if all have it set).