Is it possible?

There’s readers for the free iBooks I think. Most paid-for iBooks are DRM-protected which will leg up non-iDevices.

Might be worth a punt playing with Calibre to try and convert them to something more platform-agnostic. There are DRM-stripping plugins for it, though I’ve never used them myself.

I’ve tried stripping DRM out of purchased books with Calibre, but it wouldn’t let me do it; should I be looking for a plug-in then?
They weren’t iBook books, they were some bought through another reader, Bluefire, I think, because they have Adobe DRM, which restricts you to one or two specific readers, which is a pain. Means I’ve got books spread across four different readers.