My suggestion is only let him sleep for one hour at naptime and then wake him up and next since it is summer try taking him for a short 10-15 minute walk around the block before bedtime if possible (this works great for my active three year old), have him and your daughter explore play games, see who can run fast, who can hop and skip have them show you very physical activity like how high they can jump do stretches when you return home then give them baths and see if that helps.
I also suggest putting them to bed at different times till he gets back on track, still put him to bed at 7:30 but put your three year old to bed at 8 and see if that helps.
I know this is a lot of change but little ones routine to me never stays the same when they are that age and growing and changing the way they do, I feel like you always have to adjust "normal routine" from time to time and really wonder how other moms do it when they tell me they have the same routine for years with each child and it never varies and each child followed the exact routine as each child is born, that is something that is really difficult for me because my boys have totally diffrent personalities and behavior and I hardly do the same thing with the both of them and I'm always making tiny adjustments for summer routine, winter, spring, school starting, weekends, holidays, vacation. The best consistency we can give children is loving caring parents who can come up with a plan that best suits their child.
MAMALYN