'Should I Marry This Girl? Advise Me Please'

Good afternoon everyone..
Please I'm kindly in need of advice... ignore my typing ERROR..
There's this girl I love and I want to settle down with her. She's still in school while I'm still in school too. She's 22 while I'm 24 nd also in final YR and we both love each other..my mum has supported me to marry her.
I proposed to her and she said yes...I plan going her house next month next to start official martial rites but I'm afraid.
Here is my reasons

She's the only girl and the last daughter in a family of 5boys. Ever since we started dating, she's in 100l then, all her school burdens are on me..I take care of her and mine own...with this people around who knows about our RELATIONSHIP ask me to marry her to avoid story that touches the heart..which he has accepted , her mum nd dad have accepted it too.
My major concern about this girl is that those his brothers are not willing to do anything, istead the came asking me for small small money when I'm back, knowing fully I'm just dating thier sis....most times the my girl always feel ashamed of her brothers nd keep cursing them. The can't even call her on phone unless she calls them...nd the will keep asking why she didn't call them all this while knowing fully thier sister is in school nd not working.

I have thought about this over and over again, how do I marry from a family that can't even assist in anything...I know marriage is not always Rosy, what if something happens tomorrow nd I needed thier financial support..the can't render to me.
I discussed with my mum nd she told me I'm marrying thier sister who is well trained nd not the brother..that I can decide not to give them money again... But I'm very sad over this.
It's only the father and mum that acknowledge I hay been trying to see their sister through school expenses, including food and wears.
I discussed with my woman, she started crying, saying she knows her brothers are such a disgrace, telling me how she may commite sucide if I didn't marry her... She cried that she can't visits her house again... that her only hope will be to start prostitution which she can't see herself do that nd that's why she is going to commite sucide if I eventually leave her, all her social media handle is full with my picture, including her profile pictures.

Please what advice do you have for me.... should I let go of this girl, I don't mind letting go all I have already spent...I just want to make sure I won't regret the marriage tomorrow...I have already discussed with my mom nd we plan on going her house officially by August ending..but I'm still very worried.

Matured advice please