I don't recall the specifics on how how the service describes you allocate the sales price, but likely pro-rata to the basis is reasonable enough as long as the "long term" portion is fairly new. 

(a) If any memberunexpectedly receives any adjustments, allocations, or distributionsdescribed in Treasury Regulations § 1.704‑1(b)(2)(ii)(d)(4),(5), or (6), which create or increase a Deficit Capital Account ofthe Member, then items of the Limited Liability Company income andgain (consisting of a pro rata portion of each item of LimitedLiability Company income, including gross income, and gain for suchyear and, if necessary, for subsequent years) shall be speciallycredited to the capital account of the Member in an amount and mannersufficient to eliminate, to the extent required by the TreasuryRegulations, the Deficit Capital Account so created as quickly aspossible.

If you have an LLC or plan to create one, I suggest you consider wording that includes;No forced distributions, Non-Pro Rata distributions, No Charging Order language, Creditor cannot force the removal of a manager, No member interest can be assigned to a creditor, and Creditors have no voting rights.

I like the idea of using pro rata share among tenants based on unit size.

Do you know if the trust has a non-pro-rata distribution clause? 

It’s typically done on a Pro-rata share  based on the amount of equity invested. 

Thus, a non-member MLS fee is justified if it is are higher than that paid by members by an amount which is approximately equal to the pro rata amount of association dues devoted to the MLS.

They are taking on risk by signing on the debt, but are they guaranteeing their pro rata share of the debt?

That would get split up pro-rata amongst the investors that made that 50% contribution.That's a simple example--it can get much more complicated than that if you wish, or if that's what it takes to get the money partners interested.For example, there could be a preferred return, which means that the money investors (yourself included because you ride side-by-side with the others on the money) get 100% of the profits until achieving a specific return, such as 8% or 10%. 

CA has a LLC tax of 800 per year unless your equity exceeds 250,000 then the tax goes up pro-rata.