Can Steam bundles be split?

I'm afraid you can't, sorry.

Almost always no.

Isn't Turbo Championship Edition just the original with more stuff?

No, you can't do that.

I know about one pack, that gives You extra copies of games, if You already own some of it - it's FlatOut complete pack. I'd had FlatOut 1 and then I bought complete pack and received copy of FlatOut 1 to my inventory

I'm afraid no in most cases. The item that you already owned just disappear.

In most cases you don't get extra copies for games you already own. You will get extra copies if it's written so.
Clicky <-- more information about it.

It depends. Just add the pack/bundle/sub in your cart and it will show whether you will get extra copies of games you own or not.

Most packs/bundles like this in the Steam store will not give an extra copy of any duplicate games that you may already have.

Exceptions: Valve games generally do, and the Two Tribes bundles do as well last I saw.