Advise so far is great. Find a club. Put the other dogs up to work with this one. Check out DVG-America to find a club near you. A good club will be a real help with your training.
And, I'd add, work with the older dogs first, then put them up and work with the puppy. The older dog in my household ALWAYS comes first. She gets fed first, she gets worked first, she gets treats first. This has gone on for 5 years and it will go on for as many more as these two dogs live together. Really checks the jealousy. Old dogs, first dogs in the household need to feel respected/special.
And yes, three dogs, eh! Two are plenty of work for me. On top of that, just so you know, IPO is going to take the better part of at least one day a week. at club. Then there's the stuff you have to do at home. It's not a casual commitment.