It's already in the rules that CTs can tell Ts to get off mic, but not the whole round. A CT can order Ts off mic, even if only one person is doing that, no rules about that. The distance rule is stupid and DOES NOT EXIST, so if anyone says that's a rule just say it's not like 5 times and hopefully they'll understand.
Question, why don't you make a player complaint if someone freekills, or breaks the rules?