M.,
It sounds like your kids natural circandian rythm is that of nightbirds, and belive it or not that is normal. There are experts who say that high school is way to early for teenagers because their natural sleep patterns keep them up later, and school is earlier. Same for some younger kids (like mine). I could reccomend a behavior chart, but for bedtimes that does not always work. Some things I have found that help are 1. fresh air/exercise during the day. This gets them naturally tired. 2. I do agree with the bedtime routine everynight. 3. A story read in a soft voice to try to naturally calm them down. 4. A radio played softly will occupy their minds a little more, and may help them fall asleep. It should be just loud enough for them to hear it so that they actually have to focus on it. Right now, bedtimes are even harder because the light outside gives them more energy. As winter approaches and the days grow shorter it will be easier for you to put the to bed with less problems. But if all else fails, use the behavior chart. Have a block for every step of bedtime, teeth brushing, going to the bathroom, getting in the bed without problem, staying in bed. For each part theat they do not give you are hard time for, then they get a sticker. Set an amount like 10 stickers, and they can pick an activity, like going to the park as a family, or McDonalds or whatever. If they misbehave, complain, etc., at all, they don't get a sticker. you don't need to address the lack of a sticker, they will see and they will get the picture. I have used behavior charts with my kids at various points of their development and it has worked for me. (I worked in social services with troubled kids and they used the same kind of system with some success).
Also if you need to talk to them using I statements. Meaning don't say, "You need to go to bed..." "You are giving me a hard time..." these statements automatically cause defensiveness and defiance. Use "I" statements. "I feel tired when you don't go to sleep and that makes me feel sad." "I feel frustrated when you do . . ." "I don't like it when you do .... because I can't . . ." Stuff like that. Make sure whatever you implement you and you're husband are on the same page or they will play you one against the other.
Oh yea, one other trick. Switch to water only two hours before their bedtime, and eliminate sugar at that time too, less sugar in their systems means sleepier kids.