Your companions on the same reservation should get the same baggage allowance and boarding group. They should also get the same SDC benefit.

If this is a domestic flight, you won't get CPU in advance, as it is only allowed for you and 1 companion. If you want to try for that, you'll have to split two folks off, and then you and your companion will be eligible. If not, if you choose to split the reservation at check in to try for an upgrade, at the airport, you can designate one person as a companion to be put on the upgrade standby list with you - they should be right below you, but each will clear individually, so possible for one to clear and the other not.