1) Most wanted is ability to leave the vehicle without a gunner npc(s).
There were numerous moments when i wanted to leave my humvee to pick-up an item or to assault the cargo truck, and be able to do that with the support of the mounted MG.

I feel like NPC will do more damage that way anyway.

The most simple way i see it done, is to remap spacebar to do the same, but without a gunner(s) leaving the vehicle. Maybe make gunner leave after a second spacebar, or maybe a mod+spacebar after you already exited the vehicle. Or maybe a new keybind?

2) NPC in your squad sometimes enter and immediately quit neaby located MGs, mortars and other stuff. I'd like them to stick with deployable, but if its not possible, maybe make them not do that at all?

3) NPC sometimes does not stop at your signals (wait up), just happened again with a stolen tank.

This is already possible.

No its not. When you are driving the vehicle, you can only make your non-gunner squad leave, but you cant leave yourself.

edit: okay, apparently you can, but its not in the manual. Lify said and i confirmed: You have to mod+rmb on the vehicle (or just on the ground), then you can press space and the gunner will remain in the vehicle. I asked dio before and he said you cant

I think the AI is set to wait for you after a taxi signal only if there are seats available in the vehicle.

yep, i often park a apc beside a wounded teammate to get out and heal him while the apcs main gun covers me (if there no medic in my apc already)

just be aware that once you get inside the stolen cargo truck your squad will ditch the vehicle and try and follow you inside the cargo truck unless you ditch you squad by using the page down key

Hey, Zed, most likely I have not understood what you asked me (been busy with something else or due my English , anyway, sorry for that ), so here's the full list of commands.

By using the proper key combination* when you're in a vehicle you can enter with your squad or give them a command to do not enter/leave right after you're inside the vehicle. You can also give them a command to enter/leave at any moment.
Depending on where you are, you can give them the following commands:

1. As a driver
   - you can command them to enter/leave the vehicle and vice versa
   - you can command them to follow the vehicle
   - you can send them to any desired location (to those outside of your screen by opening the map)
   - you can command the gunner/cannoneer (in tanks/ships) where to aim (to a location outside of your screen by opening the map)
   
   You can leave the vehicle, too, and then:
   
   - you can send them to any desired location (to those outside of your screen by opening the map)
   - you can command them to follow you
   - you can command the gunner/cannoneer where to aim (to a location outside of your screen by opening the map)
   - you can command the gunner/cannoneer (all together) to abandon the vehicle
   
   
   
2. As a gunner
   - you can command them to enter/leave the vehicle and vice versa
   - you can command them to follow the vehicle
   - you can send them to any desired location (to those outside of your screen by opening the map)
   - you can command the driver where to go (to a location outside of your screen by opening the map)
   
   You can leave the vehicle, too, and then:
   
   - you can command the squad to follow you
   - you can command the vehicle's driver to follow you
   - you can send the squad or/and vehicle to any desired location (to those outside of your screen by opening the map)
   - you can command the driver to abandon the vehicle
   
   
   
3. As a passenger
   - you can command the driver (in tanks/ships, if there are gunner/cannoneer he/they start to aim at the same place you've pointed out) where to go (to a location out of your screen by opening the map)
   - you can only command the squad to leave the vehicle and you also leave
   
   When you're outside the vehicle:
   
   - you can send the squad or/and vehicle (in tanks/ships, if there are gunner/cannoneer he/they start to aim at the same place you've pointed out) to any desired location (to those out of your screen by opening the map)
   - you can command the driver/gunner/cannoneer (all together) to abandon the vehicle

NOTE

*Hotkey uses these buttons: squad command modifier + squad command + RMB/LMB
Abandonment of the vehicle isn't a new, I had read about it but I haven't used it 'till now.
For all given commands, you'll see on your screen the relevant icons showing the places where they were ordered to go, both for the vehicle and/or squad.
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just use a simple squad command to get rid of them

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