Don't put them in a low humidity environment, such as a dorm room in the winter. Don't leave the top of the cup off for extended periods of time. However, the nymphs will need a moist water wick. Make sure that it is kept moist by putting a small amount of water on the wick when needed. A small eyedropper would work well for this, but too much water may cause the seeds to mold.
Small insects are prone to damage by careless handling of the cup- be careful.
Do make sure that they are alive every day. If they are not, see us and we will give you another. The site below offers some basic life history tips on this insect, and tells you how to sex your bug when it gets a bit bigger. No more than 4 days may be missed. Summary of the biology of the milkweed bug which combines your observations with written or web-based references.