Identity and civil documents for every intended applicant, a complete personal history for vetting, evidence supporting whichever underlying immigrant classification is contemplated, and documentation of the funds. Nothing should be paid before an attorney has confirmed which classification applies and what it demands.
Vetting looks at the person, the classification looks at the record
Two different files are needed and they are often conflated. The vetting file is personal: passports, civil records for the marriage and the children, addresses and travel history, and a frank account of anything in a person's background that might bear on admissibility, disclosed to an attorney early rather than discovered later. The classification file is professional and evidentiary, and its contents depend entirely on which of the existing categories is being used, so it cannot be assembled sensibly until that question is answered.
Alongside both sits documentation of where the money came from, which any programme of this size will expect to be explicable. Ilse should resist paying a nonrefundable fee to find out whether she qualifies; the sensible order is legal assessment first, payment second.