If the G:Servant of a doctor or engineer engages an enemy (or is engaged by an enemy), can the doc/engi only use skills allowed while engaged, or whatever he/she wants while the Servant performs an idle (and eats an ARO)? The rules only talk about the options of the one being engaged, not the other one...
The Doctor/Engineer and the G: Servant trooper must declare the same Order, declaring the same Short Skills of the Order. However, it is not compulsory that they have the same target. If either trooper is not able to perform the Order (whether the Entire Order or both Short Skills of the Order), then that trooper will perform an Idle, while the other trooper will perform his complete Order normally. The controller would only be restricted if they were both Engaged. otherwise you declare the Skills you want and check who can perform it.