Sounds like a mess of a system. I have had problems exactly like that in a house I was looking after for a client. Fortunately without so many infrastructure problems. The plumber managed to fix it but once people started adjusting their room thermostats for more heat some others went cold again.
I'm sure the plumbers on here have seen a lot of this.
Maybe the plumber can help with that!
Sounds like a mess of a system. I have had problems exactly like that in a house I was looking after for a client. Fortunately without so many infrastructure problems. The plumber managed to fix it but once people started adjusting their room thermostats for more heat some others went cold again.
I'm sure the plumbers on here have seen a lot of this.