What will happen to the Ryder you don't play as? (speculation topic)

So we have these twins and you can play as either one depending on the gender you want, but what does this mean for the story exactly?

One thing I'm able to tell right away is that the fact that they're twins and both of the same ranking under their dad is by design to make the transition between which one you pick to play as, as seamless as possible, but what happens beyond that?

At some point the non-playable Ryder will inevitably do something or go somewhere on their own so they're not just passive on the Tempest or constantly being the fourth wheel in your squad (note, the other Ryder isn't a companion). Most of all, how will the Ryder you don't play as stick out as a character when we can in fact define them with our own customization in another playthrough?

Obviously, the Ryder we play as becomes the pathfinder so it's not a 2-in-1 story, but to what extend to we expect there to be unique traits for either Ryder? Is it just small dialogue changes or will there be outright different beats in the story, a la picking the Mages over the Templars's story in DA:I?

Also, let's ask the devs on Twitter when we have a good idea for one that isn't over 80 letters.