Application for Q2 Visa

Hi,

I'm planning to visit my fiance for 3-6mths stay in China, I wished to apply for the Q2 then. My fiance and me are not married yet, the purpose of the visit is to visit her family to discuss marriage and to buy a house at the same time. Her dad is also critically ill in the hospital, we don't know how long it will drag, thus I need a longer stay.
May I know what kind of proof or letter of invitation is required? e.g. a letter written by my fiance, a letter proving her dad is in hospital, my bank account to show i have money to spend in china etc?

Lexz