Are you basing the military structure off of the United States? If so, then there's far more than one sergeant in a platoon. I'll give an oversimplification:

Sergeant (E-5) Generally a team leader, which usually consists of 4-5 soldiers. Can be a squad leader, though that is rarer.

Staff Sergeant (E-6) Squad leader, which consists of 2 or more teams, sometimes fills the role of a platoon sergeant.

Sergeant First Class (E-7) Platoon Sergeant, and the highest ranked NCO in the platoon, assists the LT

Corporals are a rarely used rank because the E-5 rank has mostly taken over their role, but technically Corporals are NCOs as well. However, it may that you're not using the US Army as inspiration, and if that's the case, I'd like to see some basic rank structure so I have an idea how the platoon chain of command works, and so forth. With that said, I saw the LT with the label of "NPC" in the CS section. If mdk doesn't mind, I won't mind making my own LT if he's just going to written off what he made as a mere NPC, once everything is cleared up.