For verbs of this type (the name is blanking atm) where they can't really have an object to act on, you instead use ~어/아 있다. 누워 있어 (lying down), 비어 있어 (empty), 써 있어 (standing), 남아 있어 (is [continuously] left).

there is an honorific version of 있다 called 계시다.
계시다 replaces 있다 in the 고~있다 and 어/아~있다 forms but for the form that shows possession 있으시 would be used.
선생님이 책 여덟 권이 있으세요 the teacher has 8 books
선생님이 생각하고 계세요 the teacher is thinking
선생님이 앉아 계세요 the teacher is sitting.

I am not positive (I'm only answering because it has been 3 months since you asked your question), but my understanding is that you would not be able to use 앉아 있으세요 for sitting because 세요 makes it an imperative (it would translate closer to telling someone "be sitting" - or just "sit down".