My youngest sister is only 21 and still in college. 

why not form a separate entity that has a broker in charge that is like a sister company that handles the sales etc therefore making you an owner so you can take the agency cut that way.  

My friends sister is a successful Doctor and bought the 40k hook line and sinker.

Two of the five siblings are willing to cooperate, one refuses to sign anything “to protect herself”, the other two will not respond to me or to my seller, their sister.

Don't tell them your budget, let them give you their price.Also, if you pay for materials, don't leave them on site or lock them up, as they might magically disappear.I speak from experience from what happened to my sister.

The most memorable was to prepare a house for my sister and her kids on short notice.  

The area has gotten rougher over the last 20 years (my sister used to live off 87th & Eastern) but if that can get turned around you'd have a real good potential to market to the folks Cerner is going to populate with.

So I called the other tenants in the building and on tenant had a hipster that his sister claimed she lost at her house two weeks earlier.

Although I am personally not a single parent, I have witnessed up close the challenges through my sister. 

We agreed, I let her out of the old lease and executed a new, signed lease agreement which listed both brother and sister as tenants.The brother has since contacted me and said that he wants new paperwork showing him as the only one living there, and adds that he understands that he is subletting from his sister.