one line to multiple

Just place one signal on the top left of the picture directly before the switch. Another one can go on the top right, about one length of a train away from the switch.
On the bottom of the picture there should not be any signal pointing downwards. There can however be one signal per track directly in front of the switch.
If you put signals in both directions in a track that is used in both directions, it will most likely result in deadlocks. Only put signal directory before cleaning the two-way track.

I guess the station is on the bottom of the picture? In this case use no signals below the switch. There are not required. Each line is assigned to a fixed platform. If you use two or more lines, they will spread across the two platforms. You can use waypoints if you want to permanently assign a line to a specific platform.
A single line cannot use two platforms (e.g. decide on a platform just when a new train arrives). It will always use only one fixed platform, as made visible in the line preview.