If I have understood you correctly...
you can say:
Sarah et toi êtes amis
Sarah et toi, vous êtes amis.
OP is asking, since you are using VOUS in the second sentence, doesn't make sense to use it in both? I.e. 'Sarah et VOUS etes amis ,vous etes amis.' I think he mistook vous (you plural) for vous (polite form).
Sign in to submit your answer
Don't have an account yet? Join today
Test your French to the CEFR standard