You can use PGM122 BTN 4 to get the Hotline (IDLE LINE SELECTION) to go to one phone, not a group.
But you can try to get - by using Preset Call Forward (PGM121) - the the hotline to go from one phone to another.
So Make a hotline for the Door phone to Station 100, make a Preset Call Forward from 100 to 101, and make a Preset Call Forward from 101 to 102.
Please try it out, and let me know your status.
Saludos...
///doktor