MultiWii

I'm sorry but I use a translator..
Are Multiwii for ATmega328 can control a drone in the system coaxial ?

Should be possible to use the Dual Copter Mix.

On the logic just as much thought, but I wanted to make sure

Maybe not plug n play but it's something to start with.

I know that the models are flying in the MW, but I think for the version with a large ATmega.

A 328 will be good enough until you start adding GPS etc.
Then it will be short of memory.
But you can easily config the setup and test to compile in Arduino ide to get a Idé of sketch size.

Yes, I know - I have quadcopter and I have no problems with the settings in the config, but I prefer to avoid changing FC

interesting design.
from that drawing it is not entirely clear how steering works - two servos to tilt the entire motor+props drive train?
You will likely face similar challenge to dualcopter: no fixed reference point for tilting the propeller plane against. Most dualcopters use some kind of stabilizer fins to reduce counter movement of the body.
good luck and keep us updated. We could help you with the mixing code if needed

I'm sorry - here a long time yet to look ..
Yes, engines and propellers work as HERE (I use a translator, and I can not properly be called ..)
Thank you for your offer of help - would definitely use : D

The elements are printed on a printer 3D, so more in a new thread