No. The official family terms cover a joining spouse and unmarried children under 21, each at an additional US$15,000 fee and US$1 million gift. Adult children have their own status and are not included.
Living near adult children is the motive, not the mechanism
Hypothetical example: a Frontenac Islands couple's whole reason for considering the Gold Card is proximity to two adult children, one a U.S. citizen by marriage and one on an employment visa. Neither is a joining family member under the official terms, which extend only to a spouse and unmarried children under 21.
The couple's own case would have to stand on its own: each spouse is either a principal applicant with a US$1 million gift or a joining spouse with the same gift plus a further fee, and the category question under EB-1 or EB-2 applies to the principal. The adult children cannot be added for any amount. Separately, the U.S.-citizen child may be able to petition for a parent as an immediate relative, which requires no gift at all and may be faster and more certain than the Gold Card for a couple whose qualifications are in hospitality.
That comparison should be made before the resort is sold. Hypothetical example: A Frontenac Islands dance-studio owner wants to include a twenty-year-old unmarried child who plans to marry next summer. The first review should confirm the child’s age, marital status, and the timing of each process step from official instructions.
A passport and birth certificate settle identity and age, while a future wedding plan may require an independent strategy. Adult siblings and married children cannot be added simply because the household can pay more.