Currently you can only have 1 expert and owner. You should be able to have at least 2 experts, as some processes are cross functional so it's useful to know who to ask.
Additionally you should be able to have a 'department' or group as the owner and within that you can have multiple people able to sign off. You don't require all to sign off just one of them.
(As is any of the manual maintenance of users, roles and responsibilities which should all be able to be done by connecting to the HR system, but it doesn't work like that).
We do not have plans to change this functionality right now, but we'll monitor interest from other clients.