Hi K.-
I wanted to address the "when my husband is not around" as my husband is a grad student and away from the house 2 nights (last semester it was 4 -so it is a common thing in our house) - when I put our daughter to bed - no issues - when he is around - chaos! He doesn't see it but he is trying to, and has started to follow my lead as he knows Kendall goes to bed for me without the chaos.
1. set bed time - we use the timer on the microwave to alert our daughter "bed time" is here. That way if she is playing, being read to, etc. it gives her a sense that when this story is done, the puzzle she is working on is done - bedtime is here.
2. bathroom time - routine it - teeth brush, hair brush, potty time, jammies then straight to her room
3. we have a ditty we say which helps our daughter focus on the fact it is sleep time -not play time (Number 1 - Kendall stays in bed! Number 2 - Kendall has dry pants, dry bed (she has a portable potty in her room); Number 3 - Kendall goes to sleep! Number 4 - mom (and dad) shut the door!) The point is it routine and it works to focus her to bed time.
4. When i put her to bed - rarely do i ever have to go back to her room.
When my husband is home, that is more common - the funny part is that when I go back in - if she is goofing around - I say "what are you giving me (toy, etc) since I had to come back in here?" - whereas my husband gets totally suckered into the back rubs, the extra kisses, the "I can't find..."
Obviously if it is for a real reason (which obviously happens) she isn't in trouble - but when she is goofing around then I seem to be the serious one.
Ironically last night she started to pull the goof routine and I said I was done, told her goodnight, gave kisses and hugs, and after prayers, left the room - for the first time, the husband followed my lead and daughter was asleep in 10 minutes with no goofing off. She slept an extra 1/2 hour this morning too - so there may be something to a "unified" routine from mom and dad. She may think Dad is the pushover but last night she realized that WE were united. Big difference.
I am not sure about the 2 kids in the same room but the other suggestions of staggered bedtimes sound pretty good.
Best of luck!