You raised a few different issues.

Clover plays to avoid getting nipped. Um, this is between THEM, you do not step in. Clover will learn how and when to deal with Loki.

They play all the time - yep, that's doggies for ya!

I want some peace = NOW you are talking training! Teach the 'settle' command and it takes lots of time and patience to build this up to 10 minutes. The younger the dog, the harder it is for the dog to learn this - just too much energy! Don't worry about separating them, or feeling sorry for the singleton. That's life and they don't see it the same way we do. You can also rotate who is off alone. Or set up a crate near you so the singleton is close to you - a GREAT thing for the pups, to be close to their pack leader! Finally, you can pull out the Kong or other long lasting chew to keep them occupied for quiet time. Still may have to keep one separated, that is fine.

They also will learn if quiet time is about the same time daily. Growing up, when we had a puppy, Mom would sit with classical music on for an hour 1 to 2 in the afternoon. The puppy soon learned she was NOT going to do anything so may as well nap. If you tend to want quiet time btween 7 and 8 PM that will work.

If you want quiet time the same time daily and that happens to be when you first get home, after having been out 6 hours daily, not going to work well. They have been resting, they are now ready to GO with their Pack Leader!!! Time for walk, run, or just time outdoors so they can play. (I don't remember your schedule, just tossing this in as an example of what will and will not work easily)