How to conjugate these phrases?

I really don't understand the following grammar structure even though I have read plenty grammar stuff (participle vs adjective..) in the internet and my old school book:

"to be interested in"
"to be accused of"

When you conjugate these phrases, do you ONLY change the word 'be' or is the whole thing just a simple passive verb contruction?
For example:

"I had been being interested in"
past perfect progressive + adjective (here interested in passive adjective form)

or does the word "interested" belong to the word "be" and signals a passive contruction?
eg. "I had been interested in" = past perfect passive voice

To bring an absurd example:
If interested is just an adjective, the following sentence should be possible, shouldn't it?

"I had been beeing been interested" = past perfect progressive passive voice + adjective

Could someone enlighten me, please. Thank you!