The necessary elements are: an express or implied agreement; a common purpose that the group intends to carry out; shared profits and losses; and each member’s equal voice in controlling the project.

I am going to guess you are doing this for more not less control of your life so maintaining control of your cash would be essential for growth and protection against unforeseen conditions. 

The place has improved a little, because Dough, Thomas, and myself have controlling interest in that those communities... don't expect anything amazing, turnover is very high, and bank foreclosures are common at those price point, so much so, we don't even buy them for that price.

This distinction controls whether you can claim all your current rental losses against your W2 income.

If the top floor becomes climate controlled storage, is that good enough to consider the building a 4-family?

Unless you invest via an LLC owned by the IRA, you will not have checkbook control over the funds which means you need to run transactions (e.g. income, expenses, etc.) through the trust company who will need time to process the transactions and generally charge fees for each transaction.

My goal would be to get that BRRRR "under control" during that period, see what I missed, lessons learned, etc., before I run off to the next one anyway...

What I have outlined here is precisely how I made the transition from SFH's to Multifamily. 

I've been reading up on rent control and I see that according to new laws, I can only raise the rent up to 8% max to account for the 5% increase and inflation. 

As things are occurring now, the bank is being paid, so they have no interest in property seizure or foreclosure, as it is a performing note, so the FIL currently has the opportunity to conduct control of it in the same way a normal person would, which should allow him to pass this via normal methods (living trust for example) to heirs, provided the payments on the note have no interruption.Am I off on any of that?