The official terms describe a separate fee and gift for each joining family member, and they do not describe a discount for adding people later. A child who turns 21 before joining is outside the published family terms, so delay carries its own cost.
Family terms are per person and age-sensitive
The published framework adds a processing fee and a gift for each spouse and unmarried child under 21 who joins the principal, including in corporate cases. Nothing on the page describes a reduced rate for later inclusion. The more important point for a Paradise family is age.
The published terms refer to unmarried children under 21, and the underlying immigrant classification has its own derivative rules with the Child Status Protection Act applying only in the manner that law provides. A family that defers a child's inclusion to spread the cost may find the child has aged out of both the program's family terms and the classification's derivative eligibility, at which point the child needs an entirely separate route. The sensible approach is to list every family member with their birthdate, confirm the terms for each on the official page, and decide with the full cost in view rather than in instalments.
Verify the family terms again before any payment.