Cosignor, multipurpose rental

[Natalie Nelson]

I am in contract for a 5 bedroom rancher in Charleston, SC. It needs some work and is technically one unit but i have ability to section off 2 bed and 1 bath to be separate and airbnb/rent. The other side is 3 bed 1 bath and is move in ready..

My aunt is a cosignor (i don't have steady income but have money to invest) and I am responsible for 100% down payment and repairs. She is expecting to make 50% of the monthly mortgage payments and eventually to receive rent income. We are getting loan as my primary residence because advantageous for interest and down payment. 

Lets estimate Unit A is 2000 sq feet. (3 bed) I plan to live there for a year to start to get property set up. Unit B (2 bed) is 1000 sq ft and plan to airbnb/rent asap.

Question 1 - I don't think I want to open an LLC, would have to change the loan to be under the LLC and i think it would change my property tax rate and might affect my ability to airbnb. Can I still write up a partnership agreement with aunt and file partnership return?

Question 2- do I claim unit A on my schedule A and unit B as 1065 with aunt?

Question 3 - i don't need her to make monthly payments (i can afford it) should I just assign her an equity% in exchange for co-signing? She is also able to vacation in the house for free. 

We will open joint account to keep track of everything. I guess this gets complicated because I'm going to live there at first. I do need to write up something saying our ownership is proportionate to our investment because its not 50/50.

Thanks for any thoughts you have!

Natalie