You sign a purchase agreement, along with the owner.  

Get an Attorney to draw up a contract for deed purchase agreement.  

I put in a purchase agreement, and am currently just waiting for financing to qualify.

Brandon, I would have 2 businesses, the properties you hold are yours, you have had them for a while, keep the flip a separate business with your partner. nothing wrong with a 50/50 deal, i am just starting a flip like that, i partnered with my Realtor/ PM, i am the money and she is taking care of the rehab. the property is 3 hours away from me and i will maybe go out there once or twice a month. i have no problem splitting the profit with her. and as far as the assistant, you may find that the flips will take up more of her time, you may want to come to an agreement as to her time allocated to each business. that will be the toughest part, she will be swamped with things to do that adding her to keep track of her time of what she is doing for both business is asking a lot of her. if you find a way to do that, great, if not maybe an agreement that the flip will pay say 30 hrs of her time where your holds will get billed 10 hrs or whatever.

Equally important, the entity needs a carefully drafted Operating Agreement (or equivalent, depending on the type of entity).

All you need is a standard real estate contract of sale agreement which both parties will get.

You can google "purchase and sales agreement for residential real estate <your county> ca."

The listing agents usually know private investors and let them know first, before the ink on the listing agreement dries.

A certified rent roll will give you the terms of of the rental agreements, the amount they are paying and lease length.  

Relevant part of Fannie guides: B3-3.1-08Rental History:NoPurchaseForm 1007 or Form 1025, as applicable, andcopies of the current lease agreement(s).If the property is not currently rented, lease agreements are not required.