Daydreamer - I won't quote your entire post, but have a couple of comments.
Keep in mind my kids are 8 & 9. One of the OP's children who is staying up until 4:30 in the morning is also 8, so although my children are not teens, my experience is relevant to this thread.
I enjoy spending time with my kids, but I also enjoy spending time with my DH without them. My kids will be living elsewhere in about 9 years, but I figure I still have another 30 years with my DH, so it is important to nurture my relationship with him.
It is not simply a matter of banishing them or not wanting to have them around.
My children do need to get up and participate in activities which happen during the day during the summer. They cannot function without adequate sleep. Besides that the entire world operates during day time hours and I want my children to interact with the world, even during the summer. They also need to be prepared for the responsibility of living a responsible life filled with work, taking care of children, etc. It's a fact of life.
Sure there are times when it is completely appropriate to stay up late and sleep late, but I would not want my children to make a habit of it.
First off, I don't know where that down thumb came from at the top of my post. I didn't use it in this post.
Well, first a few weeks each summer does not a habit make.
We all need to parent our kids at different ages, different ways. Younger kids haven't gone through that teen sleep change that teens go through.
When my older ones were your kid's ages, they needed a sleep schedule or I had cranky kids all day as they would still get up early.
Because I was able to stay home, during our pre-teen days we were involved in everything. They had a blast.
DH and I were desperate for time alone to nurture our relationship because kids that age need constant structure.
LOL, it will get better, I promise! As the boys are older now they are pretty self sufficiant.
Even with the little one, DH and I can now have lunches together (the big boys baby-sit for me), we go out to dinner and a movie, and we even had a trip to WDW alone. I had G-ma come stay with the little one and the big ones too

for that outting.
For what it's worth, we didn't have time alone until just the last few years. Well, maybe we did, DS- 3 years old didn't magically appear!
We never felt that the need for us to be alone or nurture our relationship, was more important then the short time that we had the kids at home each evening.
All's well with us, we just celebrated our 19th wedding anni on June 9th.
I promise, as the boys are older now they are pretty self sufficiant as your little ones will be in time.
Now that they are older, they do not participate in little league summer sports, for example. They have topped out of the ARC swimming classes, we love to swim and are into diving
At some point in time, you might find that the whole world is not only active in the daytime hours.
My boys video games are wireless through the Wii. The boys have to be in the house by dark, this is when the kids hook-up with their friends who also, are not allowed to roam the streets at night.
There's quite a bit of nightly activity that is safe for older kids.
The kind of activities that my boys are involved in are not affected by day or night.
They aren't just sleeping all day and playing games all night.
There's always more to the story then we can write on a message board.
They both maintain web pages, and are working on making youtube videos.
I don't mean the video silly stuff and show it, they are working with claymation, taking timed pictures and making them into a movie, working on voice overs, and so on. They are growing their brains and learning all kinds of fun stuff.
Just a note, not to you specifically, but kids are raised in a thousand different ways, no one way is better then the other, and most of them turn out to be decent, hard working, responsible adults that can handle their "facts of life".
One of my brother's is an accomplished Astrophysisist ( did I spell that right?

). His works have been published all over the world, he has traveled the globe at least two times. When he finished his schooling in America, Oxford was after him to learn there, he went, graduated, and taught classes for them.
Much like my boys, as a teen he had responsibilities beyond belief, except for summer time. Our parents let us be "us" in each stage of our lives. Summer was for exsisting not schedules. It worked for him.
Before I became a sahm, I was quite accomplished myself. I was at the top of the rat race and enjoying it every second. I lived by the clock, had all the responsibilities of a working adult and was responsible for several departments and business situations.
That's why I can say honestly, that I am much happier listening to my natural body clock. I've been on both sides. I am able to do so and that's why I allow my kids to do the same.
I have no concerns that sleeping in during the summer will affect their abilities to be responsibile adults.