adding my husband's iPhone XS to my account

What do you mean by “my account”?

• Your Apple ID? Do not do this or even consider it. Each person, regardless of age, needs her/his own Apple ID.
• Your cellular carrier account? Once the iPhone arrives, use your carrier’s methods to do this. Presumably he will get a new telephone number. Otherwise, you may be asked to supply the telephone number when pre-ordering the iPhone.

You may only order one iPhone with a given carrier per order. So if you’re ordering an iPhone for yourself and another for your husband, two orders are required. You may order both using your Apple ID. Simply do not set his up using your Apple ID.

ArdithT wrote:

I don't think he has an account.

Certainly the Apple Store folks will assist you. But in case you decide to tackle this yourself:

How to create a new Apple ID

Then:

What is Family Sharing? - Apple Support