[SBnS]

I'm french so I think I can help you but it's hard to explain and I hope there is others french here who can help too.

For "Can you tell your mother to get some food, also don't forget to ask your brother for the money", you should say like that (if you don't know the person because it shows respect)
"Pouvez-vous dire à votre mère d'aller chercher à manger, et n'oubliez pas de demander l'argent à votre frère ?"

The familiar form for "tu" and "vous" does not exist in english but in france it's different, I'm bad to explain this but I try but yes you should look to who you're telling it to.

The french is one of the hardest language to learn.