They would have to be resale contracts though, as you cannot change names on an Add-On contract when going through Disney. It would be a supplemental contract as part of your master contract and the names would have to be the same as your current master contract.
If you purchase resale, then you can have different names on the contract and it would be a totally different contract and totally different membership number. It would be managed completely separately from your existing membership, meaning you cannot combine points between the two to make reservations, for example, and banking percentages would apply spearately to the contracts and not combined.