"Master" account to check email on web for all addresses?

My wife and I have a total of six email addresses on our account. I'd like to designate one of them to be a sort of master account and be able to look at incoming messages from the other five.

I tried to log in to one of the accounts yesterday and it wanted to verify my identity.  So I typed in my cell phone number and it told me, "That phone number is already in use by another account." Well, it's our account!

We don't have any problem getting mail through a desktop client, but sometimes we may want or need to just look at incoming email through the Web site. The fact that Xfinity doesn't seem to be linking these accounts at all is troubling.

Thanks. I hope this is clear.