Children’s book: whale on cover?

I vaguely remember this being read to me in elementary school, right around 2001ish.

I think there were some quirky aunt characters (possibly witches?) and talk of some giant sea creature (possibly a whale?)

I remember the book cover showing the characters small in the foreground being dwarfed by this giant whale (or some sea creature) sticking its head out of the water.

Sorry it’s not a lot to go on, and for all I know I’m totally misremembering what few details I can think of.