My mum wants to do a POA with myself as main attorney & sib as replacement. We're getting a friend to be the "Certificate Provider" (section 10) - can they also act as a witness to my mum's signature (the "Donor") in section 9 or do we need someone else? We've been told that us "attorneys" can witness each others signature -but as we'll already have someone else there we'll probably get them to do it.