4 wl books were requested from my wishlist multiple post.  I had to deny because  of RC....  but now they went fifo-  which I didn't want to do, help!!

You need to discuss RCs before posting multiples and deals.  Now you cannot cancel until the books are accepted.  (And that is kinda nasty.  As well as a potential flag on your account.)

You can PM each person, tell them you posted it by mistake, and ask them to ACCEPT so that you can be the one to cancel.

This way, your offer isn't passed on to the next person in line, and the wisher keeps her place in the WL  line.

Or you can mail them out, of course.

If any look like they might time out: you can put your account on vacation to prevent them from going to the next person.  Just delete before coming off hold.

Is it true that if I click " I cannot mail this book" instead of "does not meet RC" , it will be removed from my shelf??

yes

ok-

I clicked "cannot mail" for the 4 books...  then last night I posted them to the original requestor's wl -   but I still haven't gotten the request for them back and they still show up on her wl page.  They also do not show up on my private bookshelf and on the transaction page it shows that they were canceled by sender but not reposted to someone else.