I'd say there is another way to show your information in order. First, merge or spatial join between two layers and make one layer, then use pop up window (Robert version!) , next, use css coding to have the information you need. To configure pop up window, you just need to select "configure pop up" on the layer in your original web map, then configure as custom, and then add very simple HTML code on that window. Esri has sample of that too : Crafting custom attribute displays in pop-ups | ArcGIS Blog