I've been watching this thread and at the moment I'm not sure where the confusion is; us not understanding you, you understanding us, confusing test results, mixing wires etc.
No blame or insults intended, just trying to get to the facts.
As I understand it you have these cables [ignoring earth] and have confirmed, by testing, that both lights are on the same MCB or fuse:
So what I'd like you to do is turn the power off, remove the switch and make the wires safe, ideally in a 4 way choc bloc in a way that the wires do not get confused or mixed up and cannot short to anything.
After finding a sensible way to identify the lights such as 1&2 or bed & bath etc, I have 5 tests for you to do by linking wires together ONE AT A TIME! in a safe way and do not confuse us with any other combinations not listed.
and fill in which lights come on in these blue boxes:
A=[ ] B=[ ] C=[ ] D=[ ] E=[ ]
Simplest way is to click on quote and fill the boxes and send, no other comments required at this time
I am expecting to see 2 or 3 boxes filled in.
For example:
A=[ 2 ] B=[ 1 ] C=[ ] D=[ ] E=[ ] or
A=[ bed ] B=[ ] C=[ bed ] D=[ bath ] E=[ ]
Please make sure you turn the power off before making changes.
If the test results are different to my prediction [not made public] then I will also be out like the others.