If I recall correctly, there's a Lemmings 2 editor about halfway done, right? Lemmings 3, not so much.
I know at least some people here either have, or at least have experienced the Acorn version of Lemmings 2, so I dunno if it's "unknown". It's not like it was unreleased. On the other hand, I didn't know they did a version for FM Towns Marty-- was that unreleased? (Kinda like the Master System version of Lemmings 2, which I'm looking out for)
Dunno about the last quesiton.