determing key

No offense, but if you can't hear if the vocals are in a different key then I suggest you seriously train your listening or pick up another hobby...

If it's your own recorded vocals that are just wobbly then you can try checking the "follow pitch" checkbox in the audio track.

 

I suspect they are not iterally in the wrong key. "out of key" is a figure of speech that means the pitch is slightly off. Or likely off on certain notes.

You can fix it but if you can't hear the problem it will be very hard, There is software you can apply to the vocal track to adjust the picth of notes that may be "off" but you can't over use it or it just sounds bad. Find some one with good ears and musical training to help. Logic has this software built-in What are you using?

Better plan is to re-record the vocals and tell the singer youwill just keep doing more and more takes until it's perfect.