The word been appears to be simply an auxiliary verb in all perfect progressive tenses (also in some perfect tenses with passive construction) and it is easy to see it that way. However, from a classroom perspective, it seems to confuse a lot of students because unlike other auxiliary verbs, been does not appear to be a finite verb as it is a participle form of "be".
They have been planning it for weeks. [perfect progressive]
All the work has been done. [perfect, passive construction]
Let me rephrase my question into two parts:
Is been an auxiliary verb in the example sentences quoted above?
If yes, is been the only auxiliary verb that can be non-finite?