You can mix but why would you do that?
Aya purists would say blasphemy for aya deonthology reasons, but chemically there is no objection. Personally I would keep them apart to get to know them apart. If feeling in for a mix experiment then I would take a bit of the mimo tea + a bit of the chacruna tea and mix those, instead of mixing a whole 10 + 90 batch. Because you cant go back or modify ratio if its all mixed already, unless you already know that this 10 + 90 is your favorite sweat spot mix of which you wont deviate from anyway. If you do the 10 + 90 then consider it good for 5 starter doses ime.
For caapi maoi the usual standard is 50 gr/dose dry wood, so you would have enough for 2 doses. You can opt for syrian rue as an alternative as you probably know.
If your water is pH 7 then no acid is needed, the plant material will drop acidity enough. Only hard (mineral) rich water might use some help from extra acid, but that is seldom.
Hope this helps.