if you mean astrologically, there's no straightforward way of knowing what could happen to them as a duo, or at least i'm not aware of any method of doing so. i have never thought to run transits for synastry charts? i don't think it's possible either? ig for their composite you could theoretically check transits but idk how that would read either.

the only thing i can really think of for astro that i would at least know how to do is to check their transits individually but even then i don't think that's what your after.

ig the way to do it would be through tarot......