I would go to 2 Nikon D610's. Don't need the MP of the 800's. Going by what your using now equipment wise. I deduce you want lower priced equipment. So, D5's and the like are out. So, I suggest a pair of D610's (don't mix systems). They have very good picture qualities, and very low light capabilities (and on sale for good price right now). If you want to save even more. Buy used D600's. Absolutely capable of very good low light portraits / weddings! I still shoot with D800 and D600 (did not upgrade to 810 or 610, not enough new capabilities to warrant it).
I shot dual systems about 15 years ago. I managed, but with buttons in different places and when you get rushed. Mistakes happens. I used dual systems way back in school in film days, but there were much fewer controls back then. Digital is different, and even modern pro level film cameras as well.