HJL,
I have thought on the topic of the home library and what books it should and should not comprise, at least in terms of there being a set of bookshelves, which all family members have access to and are encouraged to read and use for study, whether one homeschools or not.
A Bible and a good concordance thereto top the list, and I believe that the King James Version, in modern type, is generally the best overall. For intensive Scripture study, in fact, I usually print out a Book or chapters from the KJV from a reliable .pdf file. I can then underline or highlight as I see fit and can carry the pages in a binder.
I believe a good parallel translation Bible can be useful in determining the meaning of words, so long as the parallel translations are not objectionable in the intent of the translators. However, I believe there are many modern translations of good intent.
Among the Bibles I would have in my library would be a good Geneva Bible, but only if the typeface and spellings were modern while the book was otherwise complete and the notes unexpurgated. Specifically, it has to include the Apocrypha, which all original and ancient Geneva Bibles did. It’s worth noting that all KJV Bibles also did so until 1803, when a North American printing omitted it.
I would also not be without a good concordance to any translation I intended to study much from and also some supplementary literature. I would like to have a copy of Halley’s Bible Handbook, which was prepared under his own supervisions; modern ones are a farce and deviate extensively from his scholarship.
In my opinion, most really worthwhile Christian literature was published before 1900. Much of what is sold in Christian bookstores today is either empty platitudes or actively detrimental. My wife and I do not take our children to most Christian bookstores, and we do not listen to contemporary Christian music.