[Leonatus]

I'm at a book where quotations are marked by right- (opening) and left-pointing double angle quotes (» and «).
First problem: Frequently, in the middle of direct speech marked as reported, there are citations that are as well marked by right- and left-pointing double angle quotes. I would like to replace those citations by single angle quotes. Is there a good way to find them (only in the middle of direct speech, not outside)?

Second problem: It appears, that at direct speech passages, there is an opening double angle, but the closing one is missing (by error of OCR, perhaps). How can I find (and replace) such items, please?
Edit: Sometimes it's vice-versa: the closing mark is there, but the opening one is missing.

Any help appreciated!