The mold is probably powdery mildew, a common problem on all of the peas, edible and ornamental. More sun helps. Spraying them with plain water early in the morning usually also helps. The next escalation involves a mixture of organic soap and baking soda--to the tune of 1 tablespoon of soap, and 1 teaspoon of soda, to 1 gallon of water--sprayed on once a week or so. The last resort would be a chemical fungicide. As for the height, they should die down to their roots this winter. When they sprout out next spring, pinch the tips out at 1 foot and 2 feet high, to slow them down and make them bushier. That may delay blooming slightly. More sun will also make them shorter and bushier, and bring on more bloom--you might look into heading back and thinning out the surrounding shade trees and large shrubs, or moving the sweet peas.