If your question is about having a group endpoint include other group endpoints, then the answer is no. You can model a group item with a defined type as a single endpoint that would control all the items linked to that group. Or you can just setup a group on the Alexa side.
As a side note, you should set your group endpoint with a proper display category (INTERIOR_BLIND or EXTERIOR_BLIND and if using camel case format Endpoint.InteriorBlind or Endpoint.ExteriorBlind).
Group gLivingroom "Livingroom" {alexa="Endpoint.ExteriorBlind"}
Group:String gRS_living_stop (gLivingroom) ".." {alexa="ModeController.mode" ...}
Group:Rollershutter gRS_living (gLivingroom) ".." {alexa="RangeController.rangeValue" ...}
Group gRS_living1 "Shutter 1" {alexa="Endpoint.ExteriorBlind"}
String living1_stop (gRS_living1, gRS_living_stop) ".." {alexa="ModeController.mode" ...}
Rollershutter living1 (gRS_living1, gRS_living) ".." {alexa="RangeController.rangeValue" ..., channel=".."}
Group gRS_living2 "Shutter 2" {alexa="Endpoint.ExteriorBlind"}
String living2_stop (gRS_living2, gRS_living_stop) ".." {alexa="ModeController.mode" ...}
Rollershutter living2 (gRS_living2, gRS_living) ".." {alexa="RangeController.rangeValue" ..., channel=".."}