They need their own lawful basis and actual process. Immigrant-visa derivatives must enter after or with the principal.
Coordinate the actual entry sequence
A shared plan or payment does not establish residence. Assess relationships, ages and each person’s intended activity individually.
Other routes have well-settled family provisions, and it is tempting to reason by analogy: a spouse and unmarried children under twenty-one as derivatives, work authorization in some categories and not others, study permitted for dependants. Confirm which specific family members meet the official definition of an eligible spouse or child before including them in the budget or application, rather than assuming a broader family group can be included together. The current framework is set out on the official government page and its accompanying questions and answers, and that is the only source worth relying on for eligibility, amounts, process and family terms. Paying for a family member does not itself grant that person status; each person's eligibility, admissibility and, where relevant, age and marital status are assessed on their own facts, and children under 21 must be unmarried to be eligible as joining family. Separate travel dates do not necessarily require omitting an eligible spouse from initial planning, so clarify the intended application and arrival sequence.