Hi, T. ~
I'm working on potty training my younger son, who is exactly your son's age, to the day. (And my daughter is a month older than your younger son, how about that?!?!) We have a tough time with #2 as well, because he gets constipated and even when he isn't he's afraid it will hurt. I give him plenty of prune juice and put flax oil in softer foods and liquids, and then when it's time I try to distract him with a book or toy and a cool "swimming fish" lamp I've put in the bathroom. It helps comfort him and he's really proud of himself when it's all over. (We do the sticker chart thing.)
I usually leave him in a pull-up during naps and at night, and he usually wakes up wet in the morning, but is dry after the nap. So I think I'll just start putting him in underwear at naptime. He already has a vinyl cover on his mattress, so having to change the sheets won't be too bad. It's just basically trial and error. It's taken us about a month already to get as far as we have, and we're pretty pleased, actually. Our older son wasn't potty trained until he was almost four. I've learned to be more patient and laid-back about the whole thing since then as well.
By the way, where is your family located? We're in El Mirage. It might be fun to get our little ones together if we're in the same general vicinity, since they're so close in age. :) If you're interested, feel free to email me: ____@____.com.
~ R.