The problem is not well defined. In test 3 one can see that double quotes should be left alone.
As it is, solutions that only check single words in double quotes will be correctly handled, but not necessarily multiple words (sentence/s) enclosed in double quotes. An additional test should verify, for instance, that the following is correctly handled:
S1 = '"The rain in Spain"'
And of course there could be nested double quotes... A water tight definition is required her.
The letters 'w' and 'y' are actually vowels.
(Perhaps not in Cody, perhaps not even in American English - I am not sure - but for certain they are in English...)