The official FAQ says to include a spouse and unmarried children under 21 in the initial application if they intend to join. It lists additional charges for each.
Review everyone’s position separately
Provide relationship records and birth dates so counsel can assess the family plan. Do not assume that a principal’s payment covers the household or that a pending application grants work permission. Age-sensitive cases, later additions and the timing of status require individual advice beyond this public overview.
Relationship and age are proved by documents, not by household arrangements. Hypothetical example: A market research firm’s founder lists a spouse and children on an enquiry form, including a stepchild and a child close to the upper age limit. The enquiry form proves nothing; what will be read are the civil records — a marriage certificate showing the parties and the date, birth certificates naming the parents, and, for a stepchild, whatever record establishes the qualifying relationship in the terms the instructions use.
Each of those has to be obtained from the issuing authority and may need translation. Ages are proved by the same certificates, so check every date against the definition the official FAQ applies rather than against a rough recollection. Where a relationship is complicated, put the actual documents in front of counsel early; the family section of an application is not the place to discover that a record does not say what the household assumed.