The correct verbs for #1 are in the order:
Monte
Tomamos
Mandaron
Acampastes
The correct verbs for #2 are in the order:
Visitaron
Tomaron
Compraron
Regateaban
Mandaron
The answers for #3 are in the order:
Tomamos muchas fotos de nuestras vacaciones.
Nadie nos mando tarjetas postales.
Compramos unas camisetas bonitas por un bien precio
Es su camiseta.
Su is used to show possession of singular objects, in this case, a t shirt, in third person form.
