La semana pasada vosotros el uniforme todo los días.
a.
nos pusimos
b.
os pusisteis

La semana pasada vosotros os pusisteis el uniforme todos los días.

Explanation:

“Os” is the direct object pronoun that always goes right after using “vosotros”.

With regards to the verb, this has to be conjugated normally with the “vosotros” pronoun. In this case, the verb “poner” is conjugated as “pusisteis”.

On the other hand, the option “nos pusimos” would be wrong because it uses the direct object pronoun “nos” which is only used after the pronoun “nosotros”.