No. The official framework covers a spouse and unmarried children under 21, each with a US$15,000 fee and a US$1 million gift. An adult son of 24 must qualify on his own, and the farmer's status would not extend to him.
Family means spouse and children under 21, on the official terms
The FAQ addresses joining family as a spouse and unmarried children under 21 and directs that they be included in the initial application. Each of them carries the same nonrefundable processing fee and a further US$1 million gift. A 24-year-old son is outside that definition regardless of whether he still lives at home or works on the farm.
The only routes for him are independent ones: his own employment-based classification if his profession and an employer support it, a family-sponsored immigrant petition from a permanent-resident parent in the category for unmarried sons and daughters, subject to the applicable petition rules and visa availability, or a separate Gold Card application of his own with its own fee and gift. The farmer's spouse, by contrast, can join, at the stated cost. Before adding anyone, the family should ask whether each person actually wants U.S.
permanent residence with its residence and tax obligations, because the gift is not returned if the person later decides otherwise.