First you should check the shoot scripts. If they have different ones, change them so everyone has the same. There are shoot scripts where they stand still and snipe, slowly advance while firing or wait until they are really close until they open fire. Open the scripts with notepad and read the descriptions to decide which shoot scripts work best for your map.
To fully understand how shoot scripts work, you could take a look at the community guide (should be in your FPSC "doc" folder), it includes a very detailed tutorialon how to write your own enemy behaviour script.
If they allready have the same script its possibly an AI problem.
In case you find my grammar and spelling weird ---> native German speaker ^^