Who's allowed to vote when ownership is shared?

Hi

Can someone comment on the following question about voting. If myself and my spouse own a lot as joint tenants – do we both have to attend the meeting and vote? If only one of us wants to attend the meeting, how does only one person obtain the appropriate authority to represent the joint tenancy?

What if a lot is owned by 4 family members as 25% interest tenants in common and only one of them comes to the meeting to represent the interest of all the owners. How does this 25% interest owner obtain the authority to act/vote on behalf of the other owners?

Is there any difference in these rules for different types of meetings.