The arithmetic runs per head: every accompanying spouse, and every unmarried child under 21, brings with them one more processing fee and one more gift of US$1,000,000. Because that fee is nonrefundable and falls due before vetting, an unfavourable result for one member of the household recovers nothing paid on their account.
The arithmetic is per person, and so is the risk
Hypothetical example: Gisele is confident about her own position but uncertain about her husband's, and the household also includes a twenty-year-old and a twenty-three-year-old. Three things follow. The cost is calculated person by person: her own fee and gift, then a further fee and a further gift of US$1,000,000 for the husband and for each accompanying unmarried child under 21.
The risk is also person by person, because the fee is nonrefundable and is paid before vetting, so an unfavourable outcome for the husband does not return his fee. And the twenty-three-year-old is outside the definition of an accompanying child entirely, so no amount of payment brings him within the family application; he needs his own route, and that should be examined before the household commits. Sequencing questions of this kind should be put to counsel, and the current terms re-verified on the official page, before anything is authorised.