I'm beginning to hate my boyfriends son and his mother. iin?

I have been with a wonderful man for 4 years. He asked me to marry him over a year ago and I said yes. Recently, he's been wanting to make wedding plans; but I'm becoming unsure of "cementing" myself to his family because of things that have been occuring in the last year. First, we have his 15 year old son living with us 80% of the time. He has become this lazy, smartmouthed, lying idiot and we have an incident with him EVERY DAY! His father is a good disciplinarian, but this kid just does what he wants, when he wants even though he's been grounded, has his phone taken away, etc. Its getting to the point that when I open the door and see him there, I just want to leave again. Next is my bf's mother. She is constantly coming to my house asking for money, because she gives everything she has to her "favorite" daughter who is struggling right now. Mostly she's struggling because she has 4 kids but can't discipline herself from buying $200 handbags and $400 shoes. The mother gets abrasive about my bf not giving the "favorite daugther" financial help, but WTH?? She's an adult with a husband and a job; why should it be my bf's problem to support both his mother and self-indulgent sister? Not to mention that "mom" has asked to live with us a few times and I have said NO! So she whines to the rest of the family that "she can't figure me out" and that I'm probably the reason my bf won't help his sister financially. She enjoys pitting one sibling against the other to watch the drama and then plays the victim saying "I'm so heartbroken that my kids don't get along." Even though she's the one who usually starts it and then fuels it to keep going. I hate her for that. I know there is dysfunction in every family - but I find myself grinding away in my own head every day about these issues! Its to the point where I don't even know if I want to marry my bf because I don't want to tie myself into his family. Is this normal?