You got the recipe on tap (although no extra acid of any kind will be needed, as the plants themselves are rich in acidic compounds, and thus will lower pH levels; most water is acidic due to either water treatment procedures and/or exposure to carbon dioxide in atmosphere, which in turn causes water to suck it up as carbonic acid, lowering pH of most water at RT to a healthy 5.5). DO NOT USE VINEGAR. IT WILL ONLY MAKE THE FINAL PRODUCT EVEN GROSSER.
I see no reason as to why you should go through the trouble of wasting so much fresh water on two batches, when you could simply use a couple liters per wash of both plants in one pot (2 plants one cup... get it?) for a total of ~3 washes (alluding to Shulgin's Rule of Three here) to be combined before you boil it all down to make The Final Solution. There is no reason whatsoever to brew them separately; it wastes more water than you need; SantaJesusGod doesn't like it when you waste more water than you need to.
I'd suggest each participant sip a tenth to a twentieth of said final solution every half hour to an hour apart (PLEASE CHEW FRESH GINGER RHIZOME BEFORE, AFTER AND DURING THE CHUGGING. YOU'LL THANK ME LATER. Ondansetron and Benzodiazepines are also great for nausea; cannabis seems to be a hit-or-miss affair when it pertains to treating/preventing premature anahuasca-induced emesis). Keep on tripping along until your face melts off, The Golgafrinchians arrive to demolish your reality in order to make way for an intergalactic superhighway, and you can't see anything sans never ending psychedelia.
Enjoy the Freak Show,
God
'"ALAS,"said the mouse, "the world is growing smaller every day. At the
beginning it was so big that I was afraid, I kept running and running, and I was glad
when at last I saw walls far away to the right and left, but these long walls have
narrowed so quickly that I am in the last chamber already, and there in the corner
stands the trap that I must run into." "You only need to change your direction," said
the cat, and ate it up.' --Franz Kafka