murky, there are seven 9-letter answers but only one 9-letter grid space, so six 9-letter answers will need to be fitted into a shorter space, but there are only four 8-letter grid spaces, so we can infer that at least two of the 9-letter answers will have to be squeezed into a 7-letter space (or shorter), and must therefore have at least two cells containing double letters. So such cells are evidently not confined to one per entry.
That’s one of a very small number of things I’ve so far been able to work out with any confidence for this puzzle…!