Hey BP!  I have an interesting scenario I wanted to run by the forums, as I'm sure some of you have dealt with it before.  I plan on consulting with legal professionals about this, but wanted to throw it out there in case there are other ideas I should think about.
 

I have a young family out in San Diego, and my wife and I own a few properties here.  We're in position to secure another multifamily currently, but it's a little outside our price range.  I love the numbers on it, however.

Simultaneously, my mother and father (living on the east coast) expressed they would be open in the next few years to live in San Diego for 2-3 months of the year and would like a permanent place to stay.  This place would also be ideal for that given it's near our primary home, and we would still maintain some income even while they stay in it given it has 3 units.  Both myself and my father have living trusts with our respective families and children.  I have 2 sisters as well who are recipients of my father's trust.  It is a goal of my father's that if he does make a bulk investment somewhere, that all 3 of us (my siblings) be able to benefit equally from it, not just me. He doesn't want additional monthly expenses either, so needs to be short term rented the other 9 months of the year.  My wife and I do airbnb, and this property would have the curb-appeal to do that, so we'd be comfortable with this.

So I'm trying to look at creative ways to get this done.  Was looking for feedback or other methods potentially that people have done.  

Ideally, I want a scenario where my father helps with 25-50% of the down payment.  In terms of the monthly mortgage payments, I'd be open on taking all of that risk, or a higher percentage of it.  Here's some concepts.  

1) 50/50 down payment and mortgage payments and joint title in both trusts.  We split the income 60/40 (60 to us to manage and upkeep the property).  The loan would go under my wife's name with my father as a co-.  I think this can be done, but not sure.  In this case, when my parents pass, we (my family) retain 50% equity and also 1/3 of their 50% given I'm a recipient of their trust.  Then perhaps I negotiate to buy my sisters out, or just ask my dad to give me less of his other trust assets, and full rights to his 50% upon passing.  I'm not sure how complicated the taxes would be in this case though...e.g. who gets the interest deductions, expense deductions, etc.

2) Start an LLC to manage everything and give my parents some level of member ownership in the LLC. Say they put 100k down, and we put 100k down on 1,000,000 property. We could both be managing partners, but set up a governance such that we have more upside to the deal given we're managing the rentals. In this case, I would be confused how this intermingles with both of our living trusts, however. Can it be referenced in both?

Any ideas or advice welcome!