Questions about an Idea for a drivetrain.

From your drawing, you're going to have problems off the bat with amount of chain gripped by the drive sprocket. It would end up being better to just have a small loop being the 35 chain, and that loop being back motor to back wheel. From there you could put a 25 chain size sprocket onto the back, middle, and front wheels. This would mean that the back and middle wheel would have 2 sprockets each. In order to cut down on weight, you can use 25 chain for the linking of the wheels, and only use 35 for motor to back wheel transmission.

As for the concern stated about 25 chain not being strong enough, We have used it on all of our drive trains for the last 2 years, and not had any problems, as long as you design the system correctly.

One other small tip: Don't forget tensioners! Regionals are a lot more fun on the field, versus in the pit sixing a chain that popped off!