How to let a router wait for certain nodes to be finished before determining the route

[Louva1]

Hello, I have the following graph architecture, where dotted lines represented conditional edges and solid lines are strict edges. I want to run node1 and node2 in parallel because they are independent on each other. However, the router of node1 should be dependent on the output of node2, because I only want to go to node3 if node2 is deciding to go to node3 as well. If node2 is deciding to go to node4 then node1 should go to end. How can I implement this logic, without adding extra's nodes to this graph?