Well you could create a conference. All three of you would need to be using the downloaded and installed version of Yahoo Messenger. My instructions are for version 9.0, they might vary in 10 Beta or an older version.
HOW DO I START A CONFERENCE IN Y!M
1. Click Actions at the top of Y!M.
2. Click Invite to Conference. And the Invite to Conference Window will open.
3. If the people you want to invite are contacts just select their names and click Add. If they are not contacts choose Invite Other.
4. Type a Custom Message if you want.
5. If you want to have voice in the conference check that box (lower left).
6. Click Invite.