Let's say you have a set of drum brakes, same diameter drums but one has one cylinder ( 1 LS, 1 TS) and other has two cylinders (2 LS).

LS = leading shoe
TS = trailing shoe.

Let's say that the diameter of the cylinders is the same.

So when the brakes are applied, is the amount of fluid pushed into the cylinder(s) going to be that same for both set ups?

Second question.

What is it that determines how far back the brake pistons retract? Is it the spring in the master that sucks fluid back from the "brakes applied postion" to withdraw the pistons?

Ta muchly.

The piston will go back as fas as it is pushed by the spring hence why badly adjusted drum breakes and in some cases hand break ean you have a very long pedal travel.

which spring? in master cylinder or the springs on the brakes? <<--- forgot about those - so the adjuster is there to stop the spring pulling the pistons in too far then.

The sring in the drum yes, also if the hand break is out of adjustment as the hand break often works the same end of the shoes as the piston with the adjuster at the opposite end.

On front drums thet tend to have two pistons and two seperat adjusters. There are also many different types of adjusters so what I say is very general.

The springs holding the shoes under tension - they bear directly on the slave cylinder piston.