Fixed turn order

Hello. I've recently run into a problem and I'd like to ask for help.

I'm working on a very small project with an extremely simple combat system, as I need complete control for most of the things that I have planned to work properly. I've already managed how to eliminate most random events, but turn order is still giving me headaches. Basically what I want is that the player characters all have their turn in a specific order, unless they are disabled somehow in which case their turn will just be skipped, then the enemy always attacks last. After this, the cycle restarts; no double turns for anybody.

Any idea how I could accomplish this?