I can answer some of what you asked. First, X10 devices cannot be added to an Insteon Group/Scene. This is the way the Insteon architecture works, not a limitation of EZSrve. You can use the All_Lights_OFF X10 Timer option to turn off all the X10 devices. If my memory is correct, the All_Lights_OFF X10 function applies only to the selected house code so you would have to define an “all_off” Timer for each X10 house code you are using.
When you add Insteon devices to EZSrve, it asks if you want to create a link to the device. For Insteon devices where links were established, those devices are added to the Default_01 Group/Scene. What you would like to do is create a Timer that turns Default_01 Group/Scene Off. There is a minor glitch at 1.52 which does not allow specifying a Group/Scene with the”_” in the name (fixed in the next image). For now, either create a new Group/Scene with EZSrve as the Controller and your Insteon responder devices as responders, using a Timer to turn OFF that Group/Scene or create a Timer for each Insteon device you want to turn off. You can also assign X10 addresses to many of the Insteon devices which would allow the further use of the X10 All_Lights_OFF but I don’t recommend that. Lots of work and the X10 protocol is just not reliable compared to Insteon.