Well, let's work it out backwards:
Every person on your package reservations has to have the same 'status' to start. Let's say because a couple of you have APs, or some want to go to the waterparks while others wouldn't be caught dead in public in a bathing suit - you book the package with one-day base passes for everyone. While you're checking in, you upgrade various tickets to meet various criteria.
Since the CM is making changes anyway, they MAY be able/allowed to issue actual tickets to some members of your party instead of coding the admissions onto the room key. Honestly, probably your BEST answer would come from Disney. Call CRO and ask for a supervisor; see if what you want to do is possible. Because on the other hand, I can see Disney refusing - what's to stop you from trying to sell the now-actual-tickets?
As for the Grandma thing - I can't see Disney just issuing a room key for the use of someone not on the reservation. You may be able to get her one but if there are already two adults in the room you'd have to pay the additional per-person per-night cost. Or, you just may need to be inconvenienced and send someone back to the hotel with her, or have her take the baby back to HER hotel.
2trips: You, on the other hand, I think CAN get an additional room key. There's only one Disney-hotel-defined adult in that room right now; but again, you'd have to talk to Disney. They may not give you an extra room key because you already have a room.