Most babies go through 10 to 12 diapers per day when they're first born so for twins you would need to double that up which means you'd need 20 to 24 diapers per day for newborn twins.
Then as they get older the twin babies may only need 5 to 7 diapers per day so for the twins you will need 10 to 14 diapers per day for twins.
Essentially take the amount of diapers that one baby goes through and double that to get the amount of diapers per day for the twins.
So at least 24 diapers per day for newborn twins and then at least 14 diapers per day for older twin babies but they might use less diapers per day depending on the twins.