How to combine two Tado systems?

Here is the situation:
My mom had a wireless receiver directly connected to the boiler and a wireless thermostat.

In my previous apartment, I had my separate system (my own account) with several smart valves and a wireless thermostat.

Now I moved in to my mother’s apartment and she left me her system.

How do I combine her wireless receiver and my smart valves? Namely, I have issues when I add her Tado products to my account. It recognises them, says they’re connected but they simply don’t work.