Splitting a cat 6 cable through wire/cable connectors
In short, 1000baseT Ethernet doesn't work like that. All four pairs must run between two endpoints, and there's no means of handling two endpoints trying to transmit at once. Normally the architectural solution to this is to run the incoming cable to a comms cupboard "patch panel", and then two cables from the rooms to the panel, then a suitable switch plugged into the patch panel. – pjc50 Nov 20 '17 at 16:30