I’ve once bought a crate of mandarin for 2 of us, lasted more than 1 month. Towards the end of 1 month, the fruit dried up slightly making peeling a bit difficult. If you have a fridge temperature cellar, it will be better.
The fastest way to use up the fruits is to make orange juice everyday.
If your fruits are organic, dry the mandarine peels under the sun or oven, precious as spice for Asian cooking.