Welcome to BiggerPockets, Lucas! 

What I am saying is the tax bill for you could be wildly different depending on how long your partner has owned this property and how much depreciation they have taken.  

Cash flow approximately 350 a month.Option 2: Use the cash to buy land to build a 6 bed 4 bath duplex, all in cost approximately 300k/330k. 

Quote from @Simone Montague-Jackson: You can house hack with up to four units.

You may want to read up on wholesaling as a way to generate some capital.

@Bradley Buxton makes a very good point to make sure to do your due diligence as you won't be an owner occupant like your in-laws.Last bit of advice: Because this is a friendly deal, you want to take your time to make sure you structure it in a way that maximizes tax and cashflow benefits for both parties. 

I would be planning to do some things before actually making an investment.

Now, you need to figure out how to find deals and pay for them.

As someone who eventually wants to buy, I don't see that making much sense.

Would love to connect.