You can achieve that with 3DGS without any problem (network-technical wise). Especially when it doesn't have to be as accurate as for a shooter game, you can handle way more users.

You could also use Torque, which is actually build on a FPS Multiplayer engine. But it is kinda tricky to build in new content (programming wise) if you have no experience with Torque. Dunno the current price though but i bet it will handle the multiplayer part the best.

Unity is free and you can use the multiplayer functions too but i never used them before so i actually have no idea what their limitations are, but probably easy to use too.

So maybe stick with your A7 com if you only need 8 players.
But as lostclimate said, you won't come far without an experienced programmer as multiplayer is always a bit tricky.