You’re right In regards to the VA loan, one unit would have to serve as your primary residence, and it would be. There’s nothing saying you can’t charge your brother rent and share that unit with him. That would fulfill all the VA requirements. You could sleep there any night that you aren’t required to stay in the barracks or on base (e.g. weekend nights, holidays, etc). All your mail would go there, that is where you would live. But it financially will not make any sense for you to provide free housing for your brother. Once you factor in all the additional costs that go into owning a property outside of the mortgage itself you’re going to see yourself deep in the red month in and month out. My recommendation would be neither. My recommendation would be that you figure out a way to get BAH and live in that duplex full time. Whether that is working the system, making rank, or getting married. That way you are making that extra tax free money, providing yourself a cost-effective living space with your costs offset substantially by your other unit and the rent your brother pays you. Now you’re “house-hacking” and that’s where you want to be.