If separately, which one will you do first? What are your metrics to even choose? Can that choice be misconstrued as you being "unsure" that you are either poly or queer? Why give your apparently already close-minded family even more ammunition, albeit unwittingly?
... not worth the time/effort to think circles around doing them separately.
If you must, rip both band-aids off at once.
However, I think "the best kind of coming out" is not acting out of the ordinary, like my lifestyle is the most normal in the world. It's hard to attack someone who possesses the quiet confidence that what they are doing is right by them, and right by who they love.
Dating Rock and Paper.