I wouldn't do that. As I understand it, the open sleeper ticket is not subject to bucket pricing; it is always the rail fare (second-low bucket not counting Saver fares) and so there is no risk to waiting, as long as he has time to pick up the ticket. Will he leave from a staffed station? If so, it should be no problem.

Sounds good. Yes, we'd be leaving from San Diego, but since it's our return trip, I imagine I'd call to book his ticket in advance. (I'll need to book outbound flights so we'll need to know at some point in advance if he's going.)

I'd have a bit of trepidation including your father in law on the initial reservation and then trying to cancel just him. You are depending both on the clarity of communication and the skills of the agent. It appears very, very easy for a less skilled agent to trigger a reprice. You may well trigger one attempting to cancel one passenger.

Since an open sleeper reservation is a completely separate reservation, you are in no danger of triggering reprice on the original reservation by doing one. Yes, they are a pain, but if your father in laws participation is uncertain when it comes time to make the reservation, the safest thing to do is leave him off. You can always add him with an open sleeper ticket, which is a standard, if somewhat obscure, process. Cancelling one passenger on a ticket while keeping the accommodation reservation intact is not something I know about or have much confidence in.

Well put! That's what I was trying to say.

Sounds good, then the open sleeper ticket is the way to go. I'll discuss with them this weekend and hopefully make the reservations on Monday. Thanks everyone!

If the bedroom has already been purchased, will I gain or lose anything if I purchase an open sleeper ticket for my nephew now or wait until 1-2 days before travel?

I'd do it soon after you know for certain you nephew will be going, simply because there can be a lot friction in the open sleeper process:
1. You must talk to an agent to do it. Right now the wait times for a live agent can be long.
2. Not all agents understand and/or are trained in this rather obscure option. You may need to speak to a supervisor even have to roll the dice again in the game of agent roulette and call back in hope of getting a more knowledgeable agent. This could require another long wait.
3. Open sleeper tickets cannot be issued as etickets. This means no emailed PDF or Amtrak app display. A physical paper "value" is required. This means it will either have to be picked up at a staffed station, or at least at one with a QuikTrak kiosk, or mailed. If you or your nephew do not live near a staffed station, or your nephew will not be boarding at a staffed station, you need to allow mailing time.

Thanks for taking the time to respond. I forgot that open sleeper tickets cannot be purchased as E-tickets. Obviously, Amtrak's policies could change in the next 4-6 weeks, but do I need to worry that the rail fare could change substantially if I book now or later, or is it pretty much guaranteed to be the same bucket regardless of when I add him?

Are station agents also able to issue e-tickets? I have a couple trips planned, prior to traveling with my nephew, and may, try to do this at a station to cut out the opportunity for potential postal delays.

The chances of the sleeper rail fare changing are diminishing small. They stay fixed at the second coach Value bucket. They are not yield managed. In sleepers, it is the accommodation charges that are subject to yield management and can shift quickly. Inventory shifts between buckets frequently, but the buckets themselves are much more stable.

An agent at a staffed station has the capability to create and ticket an open sleeper reservation as well as a regular eticket reservation. The only thing they cannot do is make an AGR points reservation.