在英语中，”同学们买牛奶”可以表达为以下几种方式：
- The students are buying milk.
- The classmates are purchasing milk.
- Students are getting milk.
- The group is buying some milk.
- The learners are picking up milk.
- The pupils are buying milk.
- The kids are purchasing milk for school.
这些表达都是正确的，可以根据语境和语气选择最合适的一种。