Stick with an all male Guppy tank to keep the population down. My guppies have attacked baby snails and have left large ghost shrimp alone. Not sure what they'll do to baby neos.
After my guppies "unexpectedly" bred, I moved the fry and females to another tank and kept the 3 fancy males in a planted 20h. It's now going to be home to maybe 10 fancy guppies.