1. You don't move the seahorses, you just avoid them and don't suck them up in the siphon or in the turkey baster.
2. You stick the end of the turkey baster in the water above some detritus, you suck up the detritus and dirty water, and you bring it out of the water and squirt it into another container..... repeat.
What is your experience with keeping fish? Marine fish are more difficult than freshwater fish, seahorses are more difficult than most marine fish, and dwarf seahorses are much more difficult than other species of seahorses. I really wouldn't recommend dwarf seahorses as your first foray into marine tanks; they are difficult for even experienced seahorse keepers.