Tu because If you put Mi or mis son rojos it says my are red which dosen't really make sense. Since you put tu in front of son (plual) it would be they are red.
The pronoun when talking about a grandmother is abuela
Answer:
Aníbal prefiere una camisa de color rojo
Julieta y Emma quieren comprar unos vestidos
Tu tienes que llamarnos mañana
C. Ellos cruzan la Calle (They cross the street)
