You seem to be unaware of the difference between a change of leadership and a change of regime.
Kennedys death did not bring about regime change.
Killing Castro probably wouldn't have brought about regime change either.
He cites as evidence for the involvement of the British monarchy in the assassination that
JFK's limo the Secret Service car was nicknamed "the Queen Mary."
Let's leave that one all by itself.
As I said, the assassination is just an event that many people use to go after whatever demons or hobglobins they have swirling inside their heads. This person - an Irish catholic (I guess) - detests what Protestant England did to the Irish. Therefore "the Protestants" were behind the assassination.
It goes like this:
1. Protestants oppressed Catholics
2. JFK was Catholic
3. The Protestants killed JFK.
This is how children see the world.