Final answer:
The correct forms of the verb 'ser' in the sentence are 'son/son'
Step-by-step explanation:
Based on the description given, the correct forms of the verb 'ser' to complete the sentence are 'son/son'. The subject 'mi madre' is singular, so the correct form of 'ser' to use is 'es'. The subject 'mis abuelos' is plural, so the correct form of 'ser' to use is 'son'.
Learn more about The verb 'ser' in Spanish