Thanks for all the responses and suggestions.

Well, I didn't do anything in the end - I only have two sessions left at this rink and will be only too happy to get ouf of there - not so much because of those guys but because the ice is just so HORRIBLE there!
My lessons usually take place in the corner by which they stand, so that's a bit uncomfortable, but if I can, then I go to the other end of the rink as soon as they start to assemble. I really don't know what's worse at that rink, those guys or the condition of the ice!