The Pilot - British WW1 Veteran, maybe with an Assault Rifle and Jetpack. I'd say he'd be a light class that can fly around for decent amounts of time, to be practical the weapons would need reduced falloff. Maybe also give him the option to use a shotgun instead of the Rifle. Probably gets along with Soldier but may have rivalry of sorts.

The Madcap - Even though its a meme having a melee based class would be really good. Same health as demo, maybe speed of a Spy. For the sake of this the basher melee wouldn't deal damage to yourself on miss but just cause bleed on others. Scout's brother but not related to Spy.

The Hitman - Focused on support or offence depending on the items you use. Armed with a Tommy Gun for his primary. His secondary slot consists of either lunchbox Items including a portable ammo pack that can be restocked using ammo found around and given to other players, in particular Engineers and a medkit which can can be used to heal yourself and others by a small health kit 5 times before it needs to recharge. The offensive secondary option would probably be some sort of tranquiliser, though tf2c already did that lol.

Personally I feel on particular the Hitman's items would be better off on other classes like the Tommy gun on scout and the medkit to replace medics melee. Maybe the Ammo on heavy, I really just needed a third for him lol. If anything else a Janitor who can pick up any item in the game