From the current Federal Register site:
§95.1705 Individual licenses required; eligibility; who may operate; cooperative use.
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(2) Any individual who holds an individual license may allow his or her immediate family members to operate his or her GMRS station or stations. Immediate family members are the licensee's spouse, children, grandchildren, stepchildren, parents, grandparents, stepparents, brothers, sisters, aunts, uncles, nieces, nephews, and in-laws.
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It looks like they are defining it better now adays.
Craig
N1SFT
WRAE792