Change their environment from time to time.

You must clean indoor cages every week. Marmosets scentmark their cage constantly, therefore it is very important that you don't sterialize their cage at once. Clean the nestbox and the cage at different times. Use a mild desinfectant to clean their cage. They need a temperature of 20°C - 25°C in indoor cages (use also heat lamps). For outdoor cages, don't forget to provide some shade in the summertime. A humidity of 40 to 60 % is perfect. You can use moist peat (floor) to maintain a high humidity.