What is the best way to cut dry wall around pipes sticking out?

The easier way, with no math involved is to cut the new piece of drywall out to the needed dimensions. Hold it up to the opening so that it rests on the first protruding pipe, making sure the finish side is out. Give the drywall piece a gentle smack against the pipe and the pipe will dimple the back of the drywall. Using a hole saw, cut the hole, centering it on the center of the dimple. Repeat for each pipe, uming they are all different lengths. If you were careful when you held the drywall up before the first dimple and got it really close to where the opening is, your drywall piece will, after drilling for all three holes, fit right in. Good luck