Belfast City (2x weekly) and Edinburgh (3x weekly) are already available on the Flybe booking agent. The schedules are as followed:
BE1211 BHD GCI 09:50 11:25 (W.)
BE1212 GCI BHD 11:50 13:20 (W.)
BE1211 BHD GCI 14:40 16:15 (Sa.)
BE1212 GCI BHD 16:40 18:10 (Sa.)
BE1194 EDI GCI 10:50 12:40 (Tu.)
BE1195 GCI EDI 13:05 14:45 (Tu.)
BE1194 EDI GCI 09:50 11:40 (Th.)
BE1195 GCI EDI 12:05 13:45 (Th.)
BE1194 EDI GCI 14:35 16:25 (Sa.)
BE1195 GCI EDI 16:50 18:30 (Sa.)
Newcastle is yet to be released, but none of the routes appear to be a triangular via Jersey. It is pleasing to see Guernsey finally receive some additional services, and backed by local tour operators, hopefully these routes will be successful. They are untapped markets from the Island so I would imagine that there should be good demand.