First thing to make sure of with the DC-3 is that the tailwheel is not locked. It should be locked for takeoff, after you take position, and it should be locked for landing, then unlocked before you exit the runway.
If it is locked (which is the default position) while you're trying to taxi, you will have a heck of a time steering with brakes, throttle, or anything else.

The lock is a knob under the throttle quadrant- up is off, down is on.
But if the tailwheel is unlocked and you're still having trouble, it may just be your timing... it's tough with a twist-stick. Forget using differential throttle unless you have dual throttle controls- just twist for full rudder, hold that, and stab at the brake as you advance both throttles a bit (with props levers all the way forward), and you'll be able to steer well enough.
Another tip: with the DC-3, you cannot hope to pivot-turn from a dead stop with either brake engaged. Even with differential thrust. If you do get it going that way, you'll be at full power and probably have to fight to "undo" the turn.
You have to make sure you have room to get it rolling a few feet first, then "twist and stab", in small increments, and it will swing around for you.