Hi,
Just took a quick look at the AccelStepper library. It is capable of doing everything you describe without modification.
www.airspayce.com/mikem/arduino/AccelStepper/classMultiStepper.html
You will have to write code to implement it. Evidently you've already written something to control a single stepper. If you post it, I and/or others here can help you with it. Be sure to follow the forum standards for posting: forum.arduino.cc/index.php?topic=97455.0 -- specifically, scroll down to item 6 and see especially bullets 3 - 6. (You'll save yourself a lot of snark if you do.)
best,
Michael