So I am looking for suggestions on a fair way to structure such a partnership, or is the only way to do it, to have him get 50% of the profits, while me and the other guy get 25% each? 

My first questions to get answered are always:-  Do they have an existing mortgage or do they own the home free and clear (if a mortgage is present, do they need to pay it off for the deal to work)- Do they need the cash or do they want a prolonged income streamAnswers to those questions can help understand some of the key seller motivations.A typical seller financing structure would have a down-payment that would range from $10-$20K up to 10%-20%.Interest rates typically range 1-4pts over residential real estate mortgage interest ratesIf the seller wants long term cash-flow, the term can be 10yr-30yr.   

I own 3 facilities on opposite ends of the country and use a 3 pronged remote management structure that seems to work really well. 

SFH debate given the condos appear more like houses vs. boxes in a high rise.Anything specific to look out for with the ownership structure?  

I think your results speak volume for the work you are doing.Can I ask you how you structure your deals?

As well, have you ever heard of situations where the GP takes a 50% cut on the appreciation of the asset upon sale, instead of just sticking to the normal waterfall/promote structure?

That said, many realtors don't understand seller financing very well and may be skittish so they may warn their seller off.If the Seller still has a mortgage balance, seller financing is a tough sell as structuring a seller financing deal with a wrap around is complicated!   

If a buyer uses a “subject to” method to structure a deal, can they bring on a investor to help fund rehabbing etc. ?

I structured the deal so that the 4 other investors would hold the note and come up with the funds needed to purchase.

Everyone here has a different price structure plus we can see what you are starting with.