My husband and I can both experience hypomania at the same time (now and then). if/when this happens, our collective hypomania might add up to a more hypomanic episode.
One time, we went on a buying spree together -- on a whim one afternoon -- and bought too much product which could not be returned after 72 hours. That hurt our "budget" for the entire year. Lesson learned.
Generally speaking, we are both quite self-aware and also aware of one another's moods. We tend to be careful and seek "grounding" if/when we are hypo at the same time. We don't spend money on anything other than "needs" during that time. (I hope we can keep this in place.)

WC