For the owners endpoint: Only the data of the owner who approved the consent can be shared, the other account owners do not have their data shared.
For the accounts and transactions endpoint: Sharing this data depends on each owner's powers to access the account, as this access process will be replicated in the Open Finance environment.
If you need authorization from both owners to access the account normally, you will also need authorization from both owners to share the accounts and transactions. However, if a single account holder is able to access the account without the authorization of the other, only the authorization of one of them will suffice for the sharing of account and transaction data.
More information is available in the official Open Finance documentation: