Changing S2 into L visa

Hello,
I am currently staying in China on S2 type with my family. I would like to extend my visit, however i cannot provide birth certificate or any other relationship document. Suitable way how to stay longer seems getting renewal L type. Is this possible? Can I bring financial support with me in cash because i do not have chinese bank account? I am late applying (5 days before expiration date), can this infuence if i get the renewal or not?
Thank you for answers
Best regards