Too many questions from Adamawa.
If he was pdp why did he resign?
Why didnt they just impeach Nyako and Inaugurate him?
Why did Nuhu decamp?
Why did the house move for the impeachment of both the Gov and Deputy? Why not just the Governor?

I'll try to answer some of your questions based on my understanding of the politics of the state.
1. Ngilari didn't decamp to APC with Nyako. He is still a PDP member.
2. Those who plotted the removal of Nyako knew that, due to religious affiliations, it would be very difficult to remove Nyako (Muslim) and leave Ngilari (Christian) to be gov. Also ngilari and Fintiri are from the same local govt and are said to be political enemies. So Ngilari was included to make it possible to impeach Nyako.
3. Ngilari was asked to resigned in order not to be impeached. So Ngilari 'resigned' in other not to be impeached.
4. As to why Nuhu Ribadu decamped to PDP, I don't know the real reason but some say he was assured of the position of the governot by the leaders of the party. My opinion is that it is a dump move.