J.M.
Setting a timer really help both you and your child keep on track. I found when the timer rang there was no fighting or tears when it was time to go into the bathroom...and once we were in there we sat and read books or just talked until the actually went. If you just go and sit for two minutes they don't have time to relax or they know that you will give in after a minute and they will just wet themselves again...most of the time potty training is a battle of the wills, so don't give in and be consistent. Make sure to use plenty of positive reinforcement. I used stickers for #1 and jelly beans for #2 and we had the whole potty training thing licked in 5 weeks.
Start with your daughter and get her going before you start with your son, he is still a bit young and if you don't pressure him he might just decide that this is what he wants to do after watching his sister!
Good Luck!