As the other have said, welcome to teh terrible twos. It doesn't get any better when they are three either.
First of all, its normal for children to bond with another adult. Even healthy. My kids preferred my sister over me for a long time when they were this age. Took me a long to to understand that this is healthy and helps them learn to build healthy personal relationships with people other than mom and dad.
That being said, get away from your family. I was the oldest of seven kids and all my brothers and sisters were terrible at giving in to my kids behind my back. I had no authority and my son called me "hey you" or "wendi" because that's what he heard all my brothers and sisters calling me. Family time is important and they need that social bit in their lives, but you need time with just you and your child. Lots of it so that you can become "mom" again. When my family relocated to another state, it ended up being a blessing. I missed my family, I was married and couldn't of course move too, but it took away the competition and unintentional sabotaging by my family. After a year my son was calling me "mommy".
Now I'm not saying move away, I'm saying spend less time with them. You will have to put your foot down and tell your mom that you are the mother and she needs to back off. And make sure you tell your siblings the same thing. And if they cannot respect that fact, then you will need to spend less time with them because they are spoiling your daughter and it'll be ten times worse when she's a teenager if she doesn't learn to respect you now. Right now she is learning that mom's rules don't mean much, you do not want that to continue. If she cries calling for someone else, do not give in. Our children learn very quickly what will set us off and we cannot give into jealousy, anger or fear when they try to push our buttons.
Just stick to your guns and eventually you'll get past this trying couple of years and it does get better.