As the teacher in your class, you are in charge both of the music and the dancers/students. Make sure everyone knows that if dancers don’t like the speed the pianist is playing, they should talk to you first, and you’ll decide who needs to adapt to whom.
There are two issues here. Firstly, it’s about courtesy, good relations and class management – don’t let the pianist be put in a position where they have to override your judgement, or where you effectively side with the class against the pianist (“yes, slow down Mary, that’s far too fast!”). Secondly, it’s about acknowledging that tempo is a vital element of technique and interpretation that has to be embedded in your teaching: it’s not a lifestyle decision for the dancer or the pianist.
