Section 6166(b)(2)(D) provides:

(2) Rules for applying paragraph (1)

For purposes of paragraph (1)-

. . . . . . . .

(D) Certain interests held by members of decedent's family

All stock and all partnership interests held by the decedent or by any member of his family (within the meaning of section 267(c)(4)) shall be treated as owned by the decedent.

Section 267(c)(4) provides:

§267. Losses, expenses, and interest with respect to transactions between related taxpayers

. . . . . . . .

(4) The family of an individual shall include only his brothers and sisters (whether by the whole or half blood), spouse, ancestors, and lineal descendants;