Ramp for bantams

[Hokum Coco]

will they be able to travel up and down a 2-3 foot ramp,

A good rule of thumb in a perfect world:
Make your ramp twice as long as the drop which would give you a 6/12 pitch and an angle of 22.5º.
"A 4x4 block attached to the end of your ramp to make a step up will do a lot to reduce the slope also."