I have a second home that my son is living in if I add him to my deed when it comes time for him to purchase a new home will he be able to get the first home owner benefits? And how does adding a person to the deed work?

You are assuming and quessing that here will be first home owner benefits when it comes, but if you add him to the deed now, he is in effect "buying" part of the property now. He can not buy something he already owns.

Also, if there is a mortgage on the property, the lender may call the loan if you change ownership.