You may consider looking into Charlotte Mason method for ways to approach education for your children. Here are a couple resources to get you started on finding a curriculum.

https://simplycharlottemason.com/

https://www.amblesideonline.org/

There are tons of excellent homeschool curriculum available. These are a handful I'm aware of (some we use at my home). MEP mathematics can be acquired for free and offers a K - 12 program. https://www.cimt.org.uk/projects/mepres/primary/index.htm

Saxon is also a decent program. You can typically acquire used textbooks for Saxon math for very little money. The book lessons are self explanatory. You should be able to locate supplemental problems to the problem sets already in their books. Test materials from Saxon are really optional in my opinion.

Also I have found quality math instruction provided for free by qualified / capable video content creators on sites like youtube. Actually, I have downloaded while channels when I observe them to generate excellent teaching content for math concepts and logic processes.

For history, I would suggest considering providing this child with some excellent works such as "A History of England", "Our Island Story", "Our Empire Story". Literature can be accomplished easily by having your child read some of the classics. Books of poetry are also easy to come by. Commentary on the classics and on poetry is readily available as well which can assist in potentially broadening how the child thinks about the topics of the literary work.

Also, consider biographies from historical figures and if said figures were apt to write their thoughts or publish works include those (George Washington, John Adams, Thomas Jefferson, James Madison, federalist papers, anti-federalist papers, etc)

Don't forget to educate your child on economics. Personally, I ascribe to the Mises Institute, perhaps you approach that differently. There are some great classic works that would be good at some point to read. Adam Smith's "The Wealth of Nations" (unabridged version). John Locke's "An Essay Concerning Human Understanding", Hayek's "The Road To Serfdom" and "The Road From Serfdom".

Really there are a near infinite number of ways to approach education and home schooling. I would encourage you to not be afraid of screwing up your child's education. Don't try to patten yourself after the failing public schools which approach educating from the Prussian Model on education. The fact is there are substantially better methods and approaches available when you take ownership of educating your own children.

Good luck to you and your friend.