There appears to be 2 options. 1 create a ring group with the members or 2 create a phantom extension and put either a keyline or multicall key on the desired sets. Then forward either to the hunt group access code or extension.
Valid call forwarding destinations are: Dial 0 access code, night bell, LDN’s, hunt groups (not data or modem pooling type), industry-standard telephones, SUPERSET telephones, Mitel IP telephones, consoles, ACD Paths, personal speedcall keys, system abbreviated dial numbers, or personal speedcalls.