Okay, first off the Family Bedroom only works if you have small children. Two of the berths are short and small and designed only for children.
You are correct in that there is only one family room. The Portland section is generally only one sleeper (they put on a second Portland sleeper the summer of 2019 only for the first time in memory, and I don't think it is coming back) and there is only one family room per Superliner sleeper.
Based on Niemi24s charts, and allowing that they are not fully updated, and also assuming one adult per room and one half fare child under 12 per room, the roomette accommodation charges appear to be in the highest bucket. The Bedroom accommodation charge also appears to be in the highest bucket.
It is really early to be booking for July 2022. Amtrak no longer routinely releases inventory at low bucket 11 months in advance, so the old "buy 11 months out and get low bucket" rule of thumb has been gone a few years now. Now the appear to be releasing inventory based on an optimistic projection of demand for the period of travel, then adjusting as time goes on if necessary. Which is smart if they do it well, but how well they do it is questionable.
I checked the the fares CHI-PDX leaving Chicago the Monday before Thanksgiving for arrival the day before Thanksgiving and got $4279 for 2 adults and 2 children under 12, which appears to be the second highest bucket. The same for leaving 12/21 and arriving on 12/23. For July 12, 2022, I got $5003, which appears to be high bucket. My point is that even during a high travel demand period, but one that is closer, the rates are lower. That indicates to me they've adjusted inventory allocation at some point.
I could not replicate your fares exactly on Amtrak.com, most likely because your actual point of origin may not be Chicago. The difference is not accounted for by assuming one child is over 12 (which would be a 123.50 difference).
With all that said, my point is that the fares may well drop. I'd start looking again in a couple of months to give Amtrak yield managers some time to track trends and react. You wouldn't be losing anything, fares are at high bucket already, so there is nothing good to grab. I would not worry that much about inventory, the Thanksgiving and Christmas dates I just checked still have availability in both roomettes and bedrooms. But also bear in mind that July is a peak travel period and it is highly doubtful they will ever drop as far as low bucket. Middle bucket is probably about the best you could hope for.
Another option would be to check going through Seattle and then taking a Cascades train to Portland. The Seattle section generally has two sleepers in high demand periods, making for two Family Bedrooms.
Finally, as to your other points:
1. There is no Business Class on the Empire Builder. Even if there were, like on the Starlight, the seat pitch is no different, since they use a Superliner coach with better upholstery for Business Class on Superliner trains that have Business Class.
2. As it stands now, the dining car is off limits to coach passengers. There is no indication at all about when, if ever, coach access to the dining car will be restored. It may be by next July, it may not. I wouldn't count on it, though.
