This response has you covered (it’s from the lead dev), since the feature is in alpha if I’d recommend joining their support group if you need further details.
A more reliable form of communication - #20 by ossguy
On the group chat question, to start a group chat it’s as was said: you use the Jabber ID of +1...,+1...,+1...@cheogram.com (numbers separately by commas) for the contact. To answer another sub-question, if you sort them in increasing numeric order, then replies will come back on the same Jabber ID.