Final answer:
The claim that affinals include siblings, nieces, and nephews in lineal kinship is false. Affinals relate to marriage, while siblings and nieces/nephews are consanguineal ties.
Step-by-step explanation:
The statement that affinals in a lineal kinship terminology system includes siblings, nieces, and nephews is false. Affinals, by definition, refer to individuals that are related through marriage or mutual agreement, not through blood or descent. Therefore, siblings, nieces, and nephews, fall into a different category known as consanguineal ties, which represent biological or "blood" relationships. Lineal kinship focuses on the nuclear family and differentiates between nuclear family members and other kindred by using less individualized kinship terms for the latter, stressing that rights and responsibilities are primarily concentrated within the core family unit.