i would think if they need/want you to be there, they will request your presence within the interview letter when/if it comes... you could go with him physically to the embassy, but there is no guarentee they will let you in the room if they aren't interested in interviewing you directly... in that case you'd just sit and wait for your father to come out... some offices/VOs will entertain other applicants/sponsors if they are accompanying the interviewee, others are very strict about who they want to talk to... if it comes down to them wanting to interview both of you, they may want to talk to the two of you together or one at a time...
taking a wild guess here, but if this might be a language concern on your father (or your) behalf, its best to arrange a translator just in case... they probably won't let you translate for him...
