Second hub for a seperated building

I’m currently running HA on Raspberry + Conbee II.
I’d like to put a couple of door sensors into a cellar which is about 20mt away from my house (where HA lives); the buildings are separated by a garden but they share the same lan.
I think that using a zigbee repeater is out of the question…
I read that in such cases one need to use a second coordinator and create a separate mesh… but what do I need specifically? Can both zigbee network be managed by the same HA istance?