How to apply Macau Visa when a Vietnamese traveling in Hong Kong?

My family and I will visit our relatives in Hong Kong in April. If they have time, they will guide us to Macau two days trip, but my mom and brother are from Viet Nam, they need to apply a Macau Visa . So, I wonder if they can apply in Hong Kong? If yes, what document do they need beside their Passport? They have already got multi Hong Kong Visa. what's more, I want to know where to apply, how long the time to wait, and how much the fee is? Thanks!