You mentioned your DH having to wake up early sometimes and the kids seeing/hearing him in the early morning. Did you mention where the children sleep? Are they sleeping in the same room as DH? If so, I would move them out.
My 3 year old DD also was in the habit of waking up very early, 5am, even 4am sometimes. I kept on saying to her that she needed to stay in bed until the sun came up (at least). The sun was coming up at 5:30am during part of the year, so then I changed things and did the clock in the room - she could wake up, fine, but she was to stay in her room until 7am. I told her before that was "Mommy's Quiet Time". She understands that because she has quiet time everyday after lunch.
Another thing - she doesn't nap. I know you said that nap/no nap didn't matter, but I think you need to not just look at one thing at a time here - you need a "big picture plan", incorporating many of the things suggested here.
-lots of activity in the morning portion of the day
-stop the naps, and start "quiet time" after lunch instead - in his room with some quiet music, books, quiet toys on his bed.
-earlier bedtime - you say 7-8pm now? Move it to 7pm firm. And not like this - at 7pm, we are meandering into his room - but at 6:30pm we are moving to his room, having potty break, brush teeth, glass of water, whatever, he is getting into bed by 6:50pm, hugs and kisses goodnight, time for another drink, whatever, so that by 7pm, you are walking out the door.
-bedtime routine - whatever works for you - ours is dinner, bath, chamomile tea and stories with Mommy and Daddy and Baby Sister on the couch, potty break, in bed with one more book read by Mommy, lights out, songs on the CD player, etc.
-clock in the room for morning - tell your DS he is to stay in his room until 7am with explanations as you think he will understand
-morning surprise box
-and whatever else is suggested
My point is - don't just try ONE of these things - make a WHOLE PLAN and start doing it.