Who can be on the paperwork to own the house? If my spouse/significant other isn’t on the loan can they be an owner of the property?

Anyone can be a joint owner of a property and they are not required to be on the loan application.

Only the person applying for the mortgage will appear on majority of the documents. If there is an owner of the property who is not on the loan application, they will still be required to attend the closing and sign a few documents to acknowledge the fact that a new lien is being placed on the property.