To flow two different classes on one page you will need two different flow elements. Once you have the page designed and ready to flow you are going to lock one of the flows off.
To lock a flow simply click on Arrange > Lock/Unlock > Lock All. This will lock the flow and prevent portraits from flowing into that element. Make sure you keep the other one unlocked because we are going to flow to that element first.
Once the top element is locked, we are going to flow to the bottom element. Make sure to select the Category you want to flow at the bottom, in this case, we are flowing the PM class. Make sure the Start and Stop are set to the page you want to flow on. Then click on Flow.
Now that the class is flowed we need to unlock the top and lock the bottom element. Click on the top Flow Element and then click on Arrange > Lock/Unlock > Unlock All. Then we are going to lock the flow element we just flowed to. This will block off this element.
Once the top Flow Element is unlocked and the bottom is locked then you can flow to the top element. Just do the same here as you did with the first flow. Make sure you have the correct category and make sure the start and stop are set to the same page. and then click on flow.
There you go, you now have two classes flowed onto one page.