Instead of taking the trouble to mix  2 flavours  here is an idea for you, the 2 headed or 3 headed shisha bowl.
“Aywah, Saet-Safa”
Even better, if you mix two different brands in one regular bowl ,lets say Nakhla mint with al-waha chocolate, you will not be succsessful. Why? Each has a different ammount of glycerin.AlWaha much more than Nakhla. It will make for an uneven burn, but you can do such if you put each separately in their respective bowls with no actual mix. The resulting mix is when both come down the middle  tube.
I’ve never tried the 3 head, and never mixed 3 flavours. Its an option if you want.
Here is the link
Don’t be a monkey, buy your own hookah.
Hookah 1