Now I know that all students talk in class. I am in a class where a group of students will talk no matter what is going on in the classroom. A teacher could be teaching, students sharing reading aloud, administration talking to the class, important announcements on the intercom, or even testing. These students will talk through anything and will make it a point to talk over the teacher when they are talking or trying to redirect the students. I have moved these students, written them up, and contacted administration, I am not sure what to do any more to get these students to get disrupting my class.
Behavior management and parental involvement are both good solutions. I would also advise asking the administration for their help as well, since this is more than just during teaching. This could be a potential safety hazard. Having two forms of backup would be the best idea.
I have been in classrooms just like this. I do believe that expectations should be reviewed every morning followed up by consequences. Recess is not a guarantee but the students love it. One time I wrote the word RECESS on the board and every time I was interrupted by students talking, I would not say anything, I would just go over and erase the letter R and so on. Students knew that if I erased the entire word RECESS that they would be sitting at their desks reading or doing work. It usually took until I got to the second to the last letter that they started to realized that I meant business and stopped. Good Luck!
I would suggest try to talk to administration and see what ideas they have. Maybe try other activities or work with the parents?