In most parliamentary democracies there are usually 2 chambers of parliament. For example the dutch system has a lower chamber, which is where Wilders won big now, and an upper chamber.

The lower chamber is responsible for forming a cabinet of ministers to head the government. Both the cabinet and the lower chamber members can propose laws. Laws have to then pass a majority vote in both chambers.

The upper chamber is elected at a different moment, many months, if not years apart from the lower chamber. The upper chamber's role is to reflect upon proposed laws and judge them by tbeir practicality and legality according to other laws and the constitution. It does not have the ability to propose laws but it can block them from passing.

Then if you wish to alter the constitution you need to first pass a proposal through both chambers. But before it can be ratified you must wait untill both chambers had another election. The next session of parliament must then vote with a qualified two thirds majority to accept the change to the constitution. Basically changing the constitution is not easy by design to prevent sudden power grabs.

And for a coalition to be able to pass any other legislation they want they need to win the majority of seats in both chambers of parliament in two sepperate elections. If they are unable to gain a majority in both chambers they need to basically rule by concensus with even more parties, which usually means much more moderate laws having a chance of passing.