Check in and baggage allowance will be premier access and 2x70lbs if any segment is in F. The boarding pass for the Y segment will not show premier access for the first segment however, and the seating group will be 3/4/5 depending on window/middle/aisle.

As others have said, bring them with you, with the exception of Chicago (where the security line dragons make the PHX UC dragons look like Dora the Explorer) I've never had anyone even question the "s/he's with me" statement (and in Chicago they just wanted to make sure we were on the same flight).

P.S. I would argue they could also board with you as the policy is simply that those traveling together board with the lowest group#. That said I could totally see a GA getting huffy that you aren't seated together and thus she has to wait (and then I've seen countless other GAs not care to check).