Going back to original post, we wanted flexibility to travel whenever
and wherever we want, to travel in first, to not have to run to trains
all the time when we can simply take the next one as it's a flat-rate,
all-you-can-ride pass. And no, we're not moving every night. The plan
is four main cities in 15 days where we use the cities as hubs from
which to travel (via train) to anything and everything we want to see
In that context the German Rail Twins Pass 15 Consecutive Days makes
Well, it makes sense to you. I of course read your original post. And now that you've posted a vague outline of your intentions ("4 main cities in 15 days where we use the cities as hubs from which to travel...") I am pretty confident that you are still somewhat confused and/or in the dark about how transportation in Germany actually works... and about how you will do outings from your hubs.
Knowing the other transportation "wizards" on this forum, I think most would likely agree that your railpass of choice is pricey overkill for the nature of your plans. But they can speak for themselves.
Your chosen German rail pass is in fact very unlikely to get you to all the places you want to go; unlike the Bayern Ticket Day pass, the MVV day passes/tickets, and day passes in other metropolitan centers around the country, the GR Twinpass is useless for travel on the subway, streetcar, and bus systems which you will need to use if you are visiting sights in/near main cities like Berlin, Munich, Hamburg, Stuttgart and numerous others. A couple can travel to multiple points all day long in such places with these day passes. They are what you said you wanted - "flat-rate, all-you-can-ride" passes. AND... the local/regional day passes for these transport options ALSO provide TRAIN transportation for outings like the ones you have in mind. So even if it's only trains that you need to get to a certain place, with a rail pass, you're often riding the exact same trains the day passes use, but you're paying more per day. And then you will have to buy ADDITIONAL tickets to fill in the public transport gaps that the rail pass creates for certain destinations.
As far as the itinerary, how many days, where we are staying, etc.,
etc., none of that is relevant.
It absolutely is relevant for the trip outline you provided, assuming that things like convenience, price, and actually reaching your day trip destinations are things that matter to you. If your goal were just to ride trains somewhere, anywhere, every day or almost every day, and maybe for most of the day, then the rail pass strategy you have now wouldn't be that bad a plan.
Not trying to be nosy about where you'll be in Germany - that's no concern of mine - just trying to respond to your post, which sadly calls for a solution that's more complex than the "railpass-only" solution you were hoping for.
Post more-specific plans if you want a transport strategy that will actually get you around as you hope to do.