I asked around on this one and there is agreement that this is one of the few cases in which this print material is not appropriate for braille. There is no way to describe the pictures without giving away the answer. I think your TN is excellent but in this case, unnecessary. The page can simply be omitted with a TN to say the the pictures cannot be shown in braille. You could braille the text that is there in print, but I would not include a description because the this exercise and its picture can't be done in braille. If possible you could notify the agency of this situation.
There is almost always a way to modify material for use in braille, but there are times, like this one, when it just isn't possible.