1. Is it possible, 100 (or a certain number) billionaires buy 90% of the total circulation? If it is possible then 2. Will Bitcoin be able to maintain its decentralized position? Or will it be played by a small number of people like current fiat currencies?
Newbies knows how to ask questions in a funny approach

i will try to give some answers to your
questionquestions all together without having to quote each separately before saying what i have to say base on my view.
1. No, its not possible, because bitcoin is not centralized and not that there is a particular place they all have to go and buy it, those whales we also see do accumulate gradually and buy from different sources and with different time intervals.
2. Bitcoin will always remained a decentralized currency, as long as the government or any central authority are not the ones in charge controlling it.