Asterisk queue question - multiple phones for a single agent

Hello. Im a new asterisk user, and trying to figure out how to configure queues in latest Asterisk package for ubuntu.

If we have lets say three agents, each agent has a SIP office phone and a SIP mobile phone.

Agent1 has 2 SIP accounts: Agent1Mobile Agent1Office
Agent2 has 2 SIP accounts: Agent2Mobile Agent2Office
Agent3 has 2 SIP accounts: Agent3Mobile Agent3Office

Now, when a customer comes through, and is in front of the line, BOTH accounts of any agent should ring.
But when a agent has answered, lets say Agent1 got a call and answered from the office phone, the mobile phone should also be considered busy too (and vice versa, if the agent answer from mobile, his office should be busy as well), so next customer has to wait for next agent to be free.

But still, if the agent answered in the office phone, the agent should be able to make outgoing calls from the mobile, and vice versa.

How can I accomplish this?