Apple ID changing names - how do I stop this?

My wife and I use a shared e-mail account (not iCloud email). I have set up my iCloud account as "Josh & Katelyn" for the name, but am consistently running into problems with it. I have my e-mail account set up with the correct signature as well, yet I constantly see e-mails sent from the iPad or Mac as "Katelyn" for the sender instead of "Josh & Katelyn." I can't understand why it is sometimes listed as "Katelyn" when I have clearly specified it as "Josh & Katelyn" under my e-mail preferences and my iCloud settings.

Additionally, when I go to the Apple site and "Manage my Apple ID," my name is listed as my full name as specified in the billing address. If I change the name on the site to "Josh & Katelyn," this will mess up my account next time I purchase something from Apple because now the billing information is incorrect. How can I simply have any e-mails etc. always come from "Josh & Katelyn" without messing up my billing, sending from just "Katelyn" or anything else?