so the red and blacks connected are live, neutral feeding here, and then to upstairs?
That only leaves the single red not connected? That must be the switch wire.... thats all that is left.
Can you test between the single red, and the blacks to see if it changes on to off when the switches are operated?
If so, then it looks to me that the blacks are indeed neutral, goes to N of your light fitting.... the single red which needs to be tested is the switch wire and would go to L on the fitting. The bare earths, with sleeving all go together and be connected to the earth terminal of the fitting if there is one... if not, just all connected together.
The two reds that are permanent live are connected together but are not connected to the light fitting in any way... just a floating bit of connector.
Depending on the space within the new fitting, you might need to make connections away from the fittings own terminals, and run a single pig tail from these connections to L and N