I am really late in responding, but thought I would anyway because no one else mentioned "the clock."
First, if you do not want to co-sleep with your children, DO NOT start it now! It will not fix the sleep problem--just change it and if you ever want a life with your husband again, you'll be in this same spot down the road when you try to move them back into their own beds!
My now 3 year old was the best sleeper in the world until we moved her into her big girl bed at 2. That coupled with a new baby made sleeping a nightmare for me, baby and my daughter. We first tried stickers and a night-night chart. It worked so well with potty training, but not so well with staying in bed at night. My doctor suggested that he talk with my daughter. That didn't really help. My parents as teachers person discussed night terrors with me. I talked with my daughter about this and decided that she needed a stronger nightlight. She also felt much more secure when our family dog slept in her room. So now, even though he would really prefer not to do so, he sleeps in her room. It makes her feel more secure. I think this could also be done by a special night-night toy that would "protect." We also now spray "monster juice" all around her room at night to keep monsters away. (We just pretend to spray something in the room. She gets into helping spray and loves it). That helped some too.
Finally, when I couldn't take it any longer, I searched the Internet and found something that has worked for us. I found a clock. I bought it on Amazon. It works as a nightlight and is "yellow" when she needs to stay in bed. Then, at a pre-set time (for us it's 6am), it turns green. When it is green, she knows she gets to wake up. If it is not green, she has to stay in bed until it turns green. So now, we let the dog sleep in her room, we spray monster juice, we set her clock, and we pray that she'll stay in bed.
I'd say this works 85% of the time. After she's stayed in bed three or four nights in a row, she gets a special treat. If she gets up, she gets no sugary snacks the next day (not that we give her many of those anyway, but she's a cookie nut so this really kills her). This combination has really worked for us! It's not fool-proof, but it has been the best thing. The clock is great because she understands the colors and knows that she has to wait until it turns green. We get VERY excited in our house when she waits until the clock is green to get up. We make it a big deal.
We are also very consistent. If she does get up, she does not get the treats she wants the next day. I have explained to her that her actions have consequences (yes, she now knows what that means). I think we don't give kids enough credit--they can learn this. I also think it is learning time for us parents--we need to learn how to make this work and we need to teach our children the importance of sleeping--even when they don't want to learn.
Good luck. This is not a fun thing to do, but be consistent in whatever you decide to do because consistency is the key for these kiddos.
Do also discuss the issue with your doctors. They will be able to eliminate any of the medical problems that some others discussed in responses.