I would mostly agree with what Ellie suggested. It seems like your younger two are spending too much time on each subject. At that age, we don't spend more than 30 minutes a day on any subject, if that. If a longer lesson is better for timing (for example, with science), then I would do it every other day and alternate with another subject. I would also agree that if they're enjoying Expedition Earth, I would drop History or just do it lightly, say once a week with you, or just have them read books on their own relevant to the time period. They have plenty of time to get more history in.
Your 7th grader's list looks more realistic to me, and similar to what my 7th grader would do. You don't say how long is spent on math. I aim for about 45 minutes per subject at that age (although my 7th grader is mr. efficient and likes to get things done more quickly). The exception to that would be language arts, which altogether (grammar, spelling, writing, vocabulary, literature) is 1 1/2 - 2 hours.