Do people really think the royal family are that powerful
No don't be silly. This is far more likely to involve extreme wealth of the sort that makes the Queen look poor and high level political power and extreme corruption. Policital power not just meaning policiticians but the funding power behind the throne. No one donates to a political campaign for free do they.
Emphatically not talking about this case but in general terms if you were in the market to get something - anything - fixed in any prison you probably wouldn't need to bribe that many people at all - possibly 3 - or 4 at most - say one inmate(already criminal and corrupt), someone to fix the CCTV (which could probably be done externally by hacking a computer network no matter how secure) and maybe a prison guard or two to turn a blind eye.
The question really would be offering the right amount of money, picking the right people and covering the trail of both the bribery offer and explaining how it was that a prison guard on a low salary was suddenly in receipt of $1m+. The criminal fraternity I'm sure would be more than up to sorting out all of that.
Also security agencies all over the world do kill people including on foreign soil if the state security is threatened severely enough.
There's definitely enough going on here to make it suspicious. I'd cheerfully bet though that the FBI investigation will conclude genuine suicide whatever the truth. Identifying this is a hit would cause way more problems than the US political system would want.