Is there an easy way to edit multiple feature layers with an edit widget session? I want to edit two different line type elements that I want to have the same geometry. (Conduit and Fiber in the same trench.)
Currently no. You can make an enhancement request by calling tech support or adding this on the ideas site.
If you're using WAB Developer Edition you may want to look into the Batch Attribute Editor.
solutions-webappbuilder-widgets/BatchAttributeEditor at master · Esri/solutions-webappbuilder-widget...
FYI, the Batch Attribute Editor widget is tentatively planned to be added into core Web AppBuilder for the next release.
Hope this helps,
Please make this happen, pretty please