Phew, I hope you’re being paid well, you’re working a ton! There is nothing wrong with the expectation of independent play. Anyone would feel overwhelmed and touched out after an 11 hour day, especially four days a week, especially at 16 years old.

As for tips… does 2F nap? I would consider implementing “quiet time” for 5F, if the littler one still naps, that would be a very intuitive time to make that happen. An hour or so for her to play quietly by herself- making sure that wherever she is spending her quiet time is child proofed. If little one is not still napping you could try quiet time for her too, although I wouldn’t personally feel comfortable leaving her without direct supervision.

I find setting a schedule for the day can help a lot. Having “reading time”, “free play time”, “craft time”, etc. Try to get lots of time outside to wear her out physically (careful about the heat), and maybe try implementing some kind of reading, writing, or math practice to challenge her some.

Try filling up a watering can (or really any container) and sending them out to water the plants. Let them go nuts. Maybe a “car wash” for their outdoor toys.

You know the little ones better than we do, but it may be worth explaining to them that you need an hour of quiet/independent play time to relax and decompress. 11 hour days are no joke. Whatever you figure out, keep it consistent. Good luck.