I cycle with one hand.
I’ve got hydraulic brakes, and I’ve put a hydraulic splitter inline. It takes both brakes in & a single line out & then into a single Juicy brake controller. The splitter came from a quad bike setup.
I don’t find any problem with bias, nor any problems with not having enough brake fluid to shift both callipers.
For gears I have an internal Shimano Affine 8 gear hub which comes with a single controller - one button for up and one for down.
I hope that’s useful to someone. Bill
p.s. On my previous bike I had standard cable brakes. On that bike,I had taken a brake controller from tandem bike which had a cable splitter in the hand controller. This had an adjuster which allowed the back brake to bite just before the front. I don't have that bike any more so can't post a picture, but again it was a standard piece of kit, but from a tandem bike.