You can enumerate multiple channels and use the & delimiter between them.
The format for channel names is made up by Asterisk, we cannot say how channels are named. You can always check doing an 'asterisk -rx "core show channels"' when you have calls active with the device you want to track.. from the name you see remove the -asdf123asdf that is prepended at the end, that is usually a random or sequencial number.
As for call origination. FOP2 will always use the primary channel. However, there is another field you can set in buttons called "Originate Channel" that, as you can imagine, lets you specify whatever valid channel string you want for call origination. In there you can use Local/xxx type channels, that are proxy channels that maps to your dialplan. If you have an extension 100 that rings eigher SIP/100, SIP/200 and SIP/300, then you can set as Originate channel Local/100@context (where context is the correct dial plan context for that extension), and origination will use whatever device is listed via your dialplan.
All of the above except the & delimiter in the Channel field, and having the OriginateChannel available, is common Asterisk knowledge. It has no place in our documentation, you will find it in Asterisk documentation.
Best regards,
