I also have no W2 and possibly one of the highest debt to income ratios in the country.

If you are trying to raise a few hundred thousand to buy another 4-6 unit property, while I would not invest in someone with less than a year experience, I am guessing some of your pilot friends, other friends, or family members may be willing to chip in.Now, if you want to jump from a triplex to 80 units, raising 4-5mm of equity and another 4-5mm in debt, than I would just manage your expectations. 

Though it may cash flow well based on their current debt service, when you compare the income it produces to the equity they have is it actually even a good investment for them from an ROI perspective or would they be better off liquidating and redeploying?

So it depends on how many Subdivisions occur in your jurisdiction.lost another 9 months combined with the  Corp of Engineers and the local Soil and Conservation board.  

If you do, you should expect a very aggressive challenge by the IRS.At $350K of combined value it might be worth the cost to get a segregation study if you intend to keep these a long time.

I'm somewhat unusual in that I don't take on any debt.

There is no UBIT because your investment isn't leveraged with a mortgage or debt.

It is small multifamily with 30 year fixed rate debt. 

Also, how do I protect my assets if I use a solo k for a down payment but still need debt financing to purchase a property? 

Well, a lot of life happened and now I am getting back to zero no debt and I'll be renting for now and I am considering a duplex to buy cash or maybe land and some sort of unconventional home but still purchasing cash.