Am I correct in reading that the OP wants his players to rebel against authority, and is introducing increasingly-wicked royals to see what it takes?

If so, the advice given in this thread about making it personal is good: have the king take from the PCs. Demand shares of their loot.

When he's rewarding them for taking down "disloyal nobles" by making them the nobles' replacements, consider the things that the nobles rebelled over, and have the king double down on those with his new PC nobility.