I have watched this happen with people in my past. It may seem to you that they have everything, it may seem like they luck out. But they really do not. Would you rather have things and be known as a liar and a thief! That is no way to live. You work hard yes, and you do not have much, but you can have respect for the person you are. You do not have to look over your shoulder afraid that the police are coming for you. No one hides their things for fear that you will steal them. One day Karma will come back to those that cheat and lie and steal. And if you never see it happen, that is okay. You can be proud of the person you are! I think that is worth more then your mom will ever have.
You say your sister has everything! I guess not since she wanted a scum bag from McDonalds. She will mess up the relationship with her husband! And it makes me wonder about the man she married, since your mom helped them get together.
Be proud of who you are, I am