Re: to sell or not
Coolguy. The first thought I had when I started reading this, was that your sister was going to shaft you. Buy your half, and resell it immediately. For a profit.
Bob-VT has a very good idea, to lease it to her and her boyfriend, for a period of time.
However, being a Minor, she cannot buy it from you right now anyway, nor as co-owner after turning 18 can she kick you out, since you own 1/2 of the house.
You really, seriously need to sit down with your parents, and talk this out.