Investing as a limited partner/ passive investor is a somewhat risky endeavor whether it in private placement or in the public markets.  

You could pay them a flat interest rate on the funds they contribute, similar to a private lender, or offer a percentage of the profits to align their success with yours.

Hard Money Loans: These are short-term loans from private lenders based on the property's value rather than your credit score.

Strictly from a private money lens: If you're open to a 2nd position private money loan against your STR's, it's possible.

I’m still working the in’s and out’s of BP but I will try and send you a private message. 

I know I can reach out to some mortgage brokers to connect me with a private lender for most of the mortgage and then I would just need another lender to supply the down payment and renovation money.

I should note that that I was using Baselane's banking service to collect deposit and rent, and had moved the funds immediately to my private bank after I collected (thank god!).

Print them off, study them, highlight them, make notes, read some blog posts, and understand the subject.The second document he links includes precise definitions and a guide for landlords to use for screening support animals.

If it's private money, they would issue a letter.

However, depending on the Trust Company you work with, you might have more options with respect to the diversity of public and private market investments.