Hi
This is always difficult, sometimes impossible. I wonder what kind of school this is. Is there no chance to split or move students? If not, I would try to divide them into groups and let them work with different material, at least some of the time.
Cooperative learning is also a way to go; Different tasks to make them talk and cooperate together. But if some of them are real beginners, this is probably too difficult. Are you able to give the beginners some workbooks or similar to provide them with work while you engage with the advanced students? Another question; do you have computers they can use. This is a good way to differentiate. Use f.ex this site:
Activities for ESL/EFL Students (English Study)
Good luck
Greetings from Trond S