You want to create a HTTPS loadbalancer listening on the 443 port and forwarding the traffic to serves listening on different pots. The encrypted connection will be terminated on the loadbalancer from there the traffic will be sent to the Backends.
When you add the backends to the loadbalancer you will have to select the port to which you redirect the traffic for each one of them.
Therefore having 3 ports would require having three backends serving on the port 443, 444, 445.
In order to add a backend you can run the following command or edit the loadbalancer from the console:
gcloud compute backend-services add-backend BACKEND_SERVICE_NAME [...]