Final answer:
Ultima is Antonio's grandmother, and her wisdom and guidance are the reasons why Antonio's family invites her to stay with them, reflecting their deep familial bond.
Step-by-step explanation:
The relationship between Ultima and Antonio's family in the book is a deep and multifaceted one. Option (a) is correct: Ultima is Antonio's grandmother, and through this kinship, she holds a place of reverence and deep familial bond. The family invites Ultima to stay with them out of respect for her wisdom and guidance. This choice is supported by evidence from the text where Ultima's role in Antonio's life is one of a spiritual guide and healer, providing him with wisdom and helping him navigate the complexities of his multicultural heritage.