Re: How do I transfer an audiobook from my iPhone to another device?
Welcome to iMore!
Install Dropbox and then share a folder with your husband (you'll send him an email invitation and he'll install DropBox too). That's how my fiance' and I (and friends and family) share things together. I name shared folders after the people I'm sharing with. No one else but you and the other person see's what is in each folder unless you invite more people. IE; only my fiance' can see our shared folder, and only my daughter and I can see mine and her folder. Dropbox is for Apple, Windows and Android.
Edit: Someone else will have to chime in and let us know if ibooks/music bought from Apple can be shared. I think maybe the Household option, but I'm not sure how that works.