Difficult family.... Just do not know what to do anymore.....?

I have a sister that is a couple of years younger than me. Growing up, I was always independent and wanted to do things on my own but she was always dependent for everything. As kids, I took up for her but as she reached adulthood she expected me to still do everything for her and she almost flunked high school and has now become a college drop out. She cannot keep a job but expects me and my parents to support her. Now, I am married with a kid on the way and she is jealous because of the attention that I am getting. So, she went out and got herself a puppy to be her baby. Well, now that she has had it for a few months, she has outgrown the puppy stage. My sister sits at home all day watching TV and eating and sleeping. When I get home, she has her dog at my house with my dogs and she won't come get it until later on in the night because she needs to rest and cannot worry with her dog. Her dog eats everything in sight, chews on everything, and will potty everywhere in my house. I have finally gotten tired of this and told her that as long as she is home that her dog cannot come to my house because she needs to take care of her own responsibilities herself. I have only asked my family twice to watch my dogs as I went on vacation with my husband. This weekend will be the third time ever but my parents have taken up for my sister proclaiming that they always take care of my dogs. Yet, my dogs stay in a pen and all I need them to do is let them out during the day and let them in at night so they can eat and sleep. I have bought my family groceries, paid their cable and cell phone bills and everything else they can ask of me. My parents also run to me when they have a problem with my sister because they cannot understand why she acts the way she does and does not know how to handle her. I just do not know if I have done something wrong and cannot figure it out or if my family is finally taking my sister's side on everything because I went against my sister. I guess I just need some works of encouragement if there is any out there because right now I feel like I am the most horrible person in the world.