I was adopted so I know how it feels to not have anything in common with my family, and I developed inesecurities about my appearance at a young age because I wasn't anything like my perfect blonde haired sister. But I was also different than my family in lots of other ways and it always made me feel like I didn't quite belong.
I'm NOT implying that you were adopted, because there are plenty of biological families that look nothing alike and it's common for one kid out of a few to not look anything like their siblings.
My mom was the same way - all her siblings had darker skin, darker hair and never burned in the sun, while she was born with red hair and pale skin and she could never go in the sun, and they always teased her saying god ran out of ink. They made fun of her for being adopted but she never was.
But being different is not a bad thing. You are special, unique and you are your own person. You don't have to be like anyone else. Your family is going to love you despite how different you are - they may not always understand (for example, none of my family were artistic and I was. For the longest time they never encouraged it or understood my passion for art, but over the years as I got better they started to be very proud of my artistic talent, even my sister has asked me to paint her things). In time they will watch you blossom into an amazing person and they will be very proud of your own amazing personality and unique talents.
I think most siblings are usually jealous of eachother. I only grew up with one sister and we still had some sibling rivalries, but she was also jealous of me too.
But when you feel like you don't belong, the best thing to do is find out where you do belong.
Your identity as a person has nothing to do with your siblings or your parent's.
For example, my parent's were christian, but I decided to look into another culture and another belief system. They never understood it but over the years they warmed up to it and realized I was allowed to make my own choices, (choices that were not harmful to me.)
I found a way to be myself. It took quite a while of soul searching and learning and experiencing to become comfortable with who I was. I didn't need any ancestry, family history or anything like that to shape my identity.
My family are still the complete opposite of me and have nothing in common with me, and I stopped trying to change that a long time ago. I love them for who they are, and they also love me for who I am.
Just because you don't look like your sisters, doesn't mean you aren't beautiful. You have your own look, which makes you stand out and appear more gorgeous in the end. Learn to love yourself. I bet you have lots of amazing physical features that you can learn to make stand out even more, and I bet your sisters would be jealous that they all look the same and that you look different and have your own beautiful features that make you more noticable.
But whenever someone struggles with body image issues or low self esteem in regards to their appearance, it's usually because of a deeper issue. I think you should do some more analyzing about your feelings. I don't think it's the fact that you don't look like them that is really bothering you, I think it might go deeper than that. Only you know, but in my experience, whenever someone feels ugly in comparison to someone else, it's because they are unhappy with something else in their life/situation.
When I felt jealous and uncomfortable around my sister, it was never because I truly wanted to look like her or be like her, it was because I felt threatened that my parent's liked her better than me because she was so perfect and I wasn't. Ultimately that belief wasn't theirs, it was mine. They did not feel like I was imperfect compared to her, that was just how I felt because I had this fear that I wasn't good enough. I developed an eating disorder and had to overcome a lot of body image problems and confidence issues. I've written a book about how to recover and there are steps on recovering from low self esteem in general, it's a free e-book and you can download it here: https://www.smashwords.com/books/view/553489
It doesn't always have to suck when people think you aren't related to your family, that happens to me all the time and we've just learned to think it's amusing.
My mom is a short little red haired woman, and I am very tall with darker hair and olive skin. We are used to the questions "are you her mom?" but it's mostly hilarious when people try to be polite and say we look so much alike when we know they are just lying.