I'm on my phone and have no PC access, but I guess a partial answer is better than none.
You can check /rgl help
You are looking for information on the forcecombat command
I commonly use it to attack boxes in missions/etc.
I also have a manual assist button to have everyone beat up things like this that includes a nav, target, and attack/pet attack on.
That generally has nothing to do with mercs though.
All of the above will likely need to be broadcasted however you prefer to do that.