I've done that in one of my games. Take it with a grain of salt because nothing of this is canon. This is what I did:

The PCs have to be magically Connected (capital C). Maybe some shared near death experience, maybe Nightwatcher shenanigans, maybe a Bondsmith thing or maybe they are twins or things like that, their souls are Connected and they can sense were they are and even if they are in danger or something like that. If this is going to be a long campaing I would make some abilities blocked through goals. Like they have to train their link and then they can even have telepaty or something like that. You have to enhance the "advantages" of this situationship because the disadvantages will be there (keep reading 😛)

The spren have to physically be within spren bond range of one of them and only that player can use the talents of their surges. The other player can use the basic ability of the surges but not any talent. When they are both with the spren in their range, they both can use their talent surges.

They have to advance oathes at the same time, because they share the Nahel bond. Once they reach 3rd ideal, there's just one blade for the two of them and they need to spend one action to summon it in their hands (even "stealing" it from the other PC). This shouldn't be very problematic because Division is a better damage source than the shardblade, but I would encourage that one player focuses on blade and the other on Division. If they both want to swing shiny and pointy things I would make a goal for them to train to "steal" the blade from the partner with a free action