How can I convince my mom to be more supportive of me and my sisters,mainly me seeing that I will be going to NG next year?
In the end - you have to realize that your mother is her own person, she has her own faults, and can make her own decisions no matter how right or wrong they may be. She's just human.
You can try talking to her about how it makes you feel and suggest some things that she can do to make you feel more supported and appreciated. Just try talking to her - she may not even realize that you feel this way or that she is doing anything wrong. Like I said, she's just human and has a lot of things to worry about that you probley dont even realize.
If you can't talk to her - write her a letter and get things off your chest.
It's difficult to convince anyone to do anything, especially if they have it in their heads already.
Some people require proof before they offer their support. Just have patience. Eventually your mother will start to see that you intend to live your own life, and if you can show her that it's all good, the support will come in time.
Unfortunately, we can't force our ideals on anyone.