Issue with identity card after Brexit

This is complicated but I will try to explain in the hope that someone here can point me in the right direction.
My Polish wife and I (as British) have 3 children that were born in Belgium in brussels communes (Ixelle, Wolouwe) and have British and Polish registered birth certificates that state Brussels as the place of birth and not the individual commune. When asking the Polish and the UK side they state that all Brussels communes are registered as Brussels and not the individual commune. When asking what will happen on the change of ID cards to type M or if we could change their nationality registered on the ID to Polish they say that this can only be done if their birth certificates and passports contain the actual commune and not the general Brussels currently on them. So we have an impossible situation as the countries will not change the information on the birth certificates and passports because they do not recognise the Brussels communes as individual and the Zaventem commune is stating that they will not change the id cards as there is a difference from the Belgium registration and the registration on the country of nationality birth certificates.
Is it just Zaventem being difficult of is this the same in all communes? Is there a government agency I could contact or does anyone know of a lawyer I could talk to to see how this could be resolved?
So much for a smooth transition for UK Belgium residents. :(
Thanks to anyone who can help me with what is causing a lot of stress in the household at the moment.

Richard