I have seen όλα change many times (e.g. όλοι).so what dictates the changes in the ending of όλ-?
The noun that it stands with -- its gender, number, and case.
Here, we have τα βιβλία which is neuter plural accusative, so όλ- needs an adjective ending for neuter plural accusative as well.
If you had read all the newspapers (which are feminine: η εφημερίδα), for example, then you would have needed the ending for feminine plural accusative, thus όλες τις εφημερίδες.
I translated this as "we read all of the books"...would this be an acceptable translation?
Yes, that is fine. Most often the Greek can be translated as either simple or continuous present.
Could this also mean "We read the whole books" (i.e. without leaving any pages out), or would this be expressed differently in Greek?
In addition to what jaye said, "the whole books" should be ολόκληρα τα βιβλία. Όλο το βιβλίο or ολόκληρο το βιβλίο is "the whole book", but for plural όλα is "all of".
Thank you. That is very helpful. I agree that "the whole books" is not right in English. It's interesting that there doesn't seem to be a simple way of saying one has read every one of the books in its entirety. In Greek, ολὀκληρος is exactly the word I was looking for.
You're right. How odd there is no way to say we have read more than one book in its entirety without using half a paragraph. Thanks for expressing it so well.