I was wondering if I could post some of my favourite recipes that I found in some recipe books?
Yes, if you acknowledge the source in a clear, identifiable manner.
I’m not the administrator of this site, so my answer is far from definitive:
If you use another source you should give credit by giving the name of the book, the author and the year of publication.
If the author finds it and doesn’t like it, they’ll write to the site and demand to have it removed.
If you’re worried about the ethics, giving credit is all you owe. If you’re worried about getting sued or getting someone sued, not likely.