Hi, I'm an international student not from UK though but I've acquired my ISEE through CAF. I am happy to help you get through this somewhat complicated process. I'm new to this website but you can write me an email or contact me on whatsapp so I can send you the document samples.
As per your question, you have to demonstrate the amount of money in the head of the household bank account as well as your household composition and his/her/their yearly income. Furthermore if any land/appartment belonging to the head of the household. All documents should be refering to the 2021 year if you plan to acquire your ISEE for this year, 2023.