Microsoft Authenticator Accounts Can They Be Shared?

Have the same authenticator app on multiple phones. For example, say my bank has 2FA, and I am using the authenticator app. Can I have the "account" tied to 2 different phones?

This absolutely is possible. I have the same TOTP authenticators on multiple personal computers (Authy and WinAuth) and across multiple phones (Android and iOS).

Can I have the same account twice?

As long as you load the secret key for the specific authenticator, you can load the same authenticator to multiple Microsoft Accounts through the Microsoft Authenticator application. For example, I have loaded the same TOTP authenticator to (Authy, WinAuth, Google, Battle.net, Lastpass Authenticator, and Microsoft Authenticator). All I needed to do was provide the secret code each application. I have synchronized more than a dozen authenticators across every single device that I use. Since 1Password supports TOTP, I have also synchronized them there.

Say both my wife and I have 2FA on our bank (same bank, different accounts). Can we have both of them on the same authenticator app?

You would have to use a different TOTP authenticator, more than likely, unless the bank allows you to provide your own secret code instead of telling you what the secret code will be. However, you could have synchronized your authenticators to any number of devices. That is the only reason I feel comfortable using them.