Unlimited Team Health:
Toggle on to try and keep all team members alive.
I haven't played all the missions, but the option works for you and the entire team
I don't know this trainer works in online mode or not, but it possible if you hosting the game.
However, please do not use trainer in online mode, it can effect offline mode in long term.
Lets me explain how, once people noticed you cheating they may post video on youtube or site boards and it surely notice by developer sooner or later. After that, they will patch anti-cheat system that check both online and offline mode. By the time you can't even use trainer on offline mode. I hope you get my point.