Date them ALL at the SAME TIME
Take them out and have fun with them as a group. Find opportunities to isolate individually (either on the night or on another occasion), and with the sexual tension going around and the fact that there hasn't been any escalation yet, they'll REALLY WANT IT. Once you get them to essentially try and seduce YOU, they'll be incredibly discreet about it.
Doing this is actually a better strategy, because if you date one of them exclusively, the other two will get jealous. Plus, if you break up with one, the other two will be off limits, and if you do sleep with another, then you'll cause a huge shitstorm.
If you're DISCREETLY fucking all of them separately, there'll be a lot of sexual tension and jealousy going around, but the girls won't be allowed to mention it or tell each other, so they'll kind of assume what's going on in the background, but not be able to call each other or you out on it.
FUN right?!