@Mason Griffin Welcome to BP and the forums!
This is awesome that you and your brother want to do this together. I think you can definitely make a great team, especially since both of you have the potential to utilize your VA loans.
Here are some of my quick thoughts:
1) You say you want to invest in real estate for passive income. Myself and I'm sure many more experienced investors would agree that real estate is almost never completely passive. Even if you make it mostly passive with management, what is your passive income goal? I'd define that first. Is it enough to quit your W-2? Is it enough to pay xyz bills? Etc.
2) Starting with a duplex is a GREAT idea, especially splitting it with someone (your twin). You'll be subsidizing mortgage with renters and splitting the rest of costs with him. AWESOME!
3) I'd definitely connect with an investor friendly agent and/or lender on here or from local meet-ups to help guide you on your loan strategy.
Hypothetically speaking, one idea you can each use an FHA loan to get properties, then move out and each use a VA loan on the next property. If you did this, you'd already have 4 properties and potentially 8, 12, or 16 units under your belt in the next 5 to 10 years.
4) Get super focused on your strategy, house-hacking, storage, etc. and concentrate your efforts on that. It is easy to get distracted, but where you focus the most attention will get results.
5) It sounds like you want to live a life by design. "Spend my days fishing" A small & mighty portfolio might be the best approach. Look up Chad Carson and his book Small & Mighty Real Estate Investor. It is one of my favorite RE investing books.
Good luck with everything!