What I can do for you
I think 90 minutes online is a great length for KS2 if the aim is to cowrite, edit and perform a poem. I would need teachers present to help with discipline where necessary as that can be hard to manage remotely with a class I’m not familiar with.
I am also happy working with larger groups, e.g. I have run 2-2.5 hour workshops with KS1 and KS2, with KS1 attending for the first hour and older KS2 students staying to edit and perform the poem.
When dealing with larger numbers (e.g. 35+ students), I need support collating the ideas and words that students generate. I have previously done this with a teaching assistant collating ideas and moving to a Google Document for the first part of the session.