Two moons with overlapping new moons and full moons once a year? So I have just begun work on my next DnD campaign and wanted a world with two moons for religious and minor plot purposes. For these same purposes, I've been trying to have the cycles of these two moons overlap once a year with a double full moon and a double new moon. 

There are some issues with doing that inherently though. Firstly, one of my moons, Umbra, is what dictates months which are 48 days long, so its cycle is 48 days as well. There are also only 8 months in a year for a total of 384 days in a year. I have been able to get a monthly overlap of both with the other moon, Luna, having a cycle of 16 days or a double new moon once a year in numerous ways but not both. 

I'm wondering if my goal is even possible and if it is, how?