Here is a picture of behind one of the light switches that is fed by the cable drop that has the three core with a twin & earth cable fed down it.
You can see the three core cable going through the rear of the back box to the two gang light switch on the other side of the wall.
The light switch on the other side of the wall is a 2 gang switch.
Ah ok - it's a twin+earth and a 3 core+earth in the conduit.
Take a picture of inside the switch on the other side of the wall, and we'll see how many cores/cables you actually need.