It seems like you are trying to explain two concepts, but aren't explicit about it.First compound subjects take plural verb forms: Sarah et ma soeur sont allées à la plage.
Second the subject pronoun changes form from its singular usage:
je --> moi
tu --> toi
Bill, I think it has appeared since you asked but for anyone wondering, but there is a lesson on using disjunctive (stress) pronouns in compound subjects and objects: Using French Stress Pronouns in compound subjects and objects (unlike English)
This, of course, complements earlier mentions - perhaps it would be helpful to link some of these (and this in those)? Given the entry test, I don't think there's a fixed order to how we encounter lessons.
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