Guillaume voyage avec ______ soeur et _______ parents.

i have to use " SON , SA, OR SES " as appropriate.

2 answers

avec sa soeur et ses parents
The possessive adjective for "his, her, its" in French is son , sa, ses. Son is for any masculine singular noun, sa for any feminine singular noun and ses for all plural nouns.

A feminine nouns like "abeille" (bee) for sound also uses "son" because "sa" would give you such an ugly sound! You might think yu are hearing s'abeille. Any feminine singular noun beginning with a vowel or a silent "h" will do that as well.

Sra (aka Mme)