Rear central locking and alarm problems

My car has been driving me crazy, I have a Mondeo 57 plate titanium x, 2l diesel. The CPU needed reprogramming before I even drove it but when you’re given it for free…

Any way a couple of days after getting it back the central locking stopped working on the rear doors, first one and then the other. It’s ok though because they still lock manually, so I thought.

Now the alarm goes off every now and then, I know, sensitive alarms aside, not really the issue. The issue is that once the alarm has sounded the central locking will refuse to lock as though a door was still open, and just to confuse me more either one or the other back doors are open. Never both together and they never relock on the button either, always manually.

So here’s my questions,

Am I looking at the individual rear locking modules, or the master one in the drivers door?

And is it just a door sensor that might be out, (usually the bonnet) or are both problems linked somehow?

Your advice would be greatly appreciated thank you.