This is a response to:
EDIT: The accepted answer works, but the bots don't do anything more than firing (no healing, no welding, nothing). I have to control them to do anything more than just firing.
Does anybody know how to solve this?
The lobby leader commands the bots. You can see this by looking on your minimap (the red lines between the leader and the bots). You have to give them a "GO" sign for them to start moving. Or a "STOP" sign for them to hold position. Other needed commands should be given by pressing the action key (E) on hackable terminals and invertory keys 1, 2, 3, and 4 for bots to do something associated with their invertory (for example to command the medic to place the healing beacon, to weld ...). Some extra options for offhand items might show up while holding the crouch key (Shift by default). To use them, press the corresponding invertory key (1, 2, 3 or 4) while holding Shift.
So for them to follow you, you should press the V key on your keyboard to give them the move command (by default).