Hello!
Since the Houses in Discovery are at war, how does that affect the trade? What do i mean: Bretonia is hostile with Kusari. Can a Bretonian trader fly in Kusari space?
Same question goes for the other houses.
Well, there are various embargoes and restrictions between Houses. Some of these may later be relaxed. For example, Bretonia and Kusari are currently at uneasy peace. This means the trade regulations may be eventually dropped.
Generally speaking:
Bretonia - trades: Liberty, Rheinland, (Kusari eventually).
Kusari - trades: Liberty, Rheinland, (Bretonia eventually), Gallia.
Liberty - trades: Bretonia, Kusari.
Rheinland - trades: Bretonia, Kusari, (Gallia eventually).
Gallia - trades: Kusari, Rheinland.
You can find which houses outlaw which imports/exports in their posted laws.
This thread contains links to all house laws (and then some), so it's a good place to start. Look for the sections in each one relating to "trade" or "commodities".