The leaders of parliament were in favor of bringing a dutch king to the throne of england because

The Dutch king (technically, "Stadholder") was William of Orange, who was married to a member of English royal family.  William's rule in the Netherlands was one in which he did not rule absolutely as a king.  Rather, the nation there was more of a commonwealth with shared power.  That's what the English Parliament members wanted.  William and Mary, coming over from the Dutch Republic, would be willing to accept a Bill of Rights which would put restrictions on the king's power.  The move to bring William over to become King William III of England became known as "The Glorious Revolution."

They made a checks and balance system to equal power within the branches. the "check" meant that one branch would watch one branch and "balance" them if they were too powerful. if you want more info on this, i would just google checks and balance system.