As an alternative, if you have access to the Gali set from 2015, you could use the axe blade(s) to do a variant of her Aqua Axes. That might be better size-wise.
Great job on all of these revamps! Lewa and Pohatu are my favorites. I might have liked Onua to be a little bulkier (his lankiness was one of the problems I had with the original Mistika set), and I think Kopaka's rifle could be a tad thicker in the middle of the barrel, where it gets a little thin (a pair of the pieces you used for the end of the scope would be perfect, IMO). Other than that, excellent job!
(Makuta Thanos sounds pretty rad, BTW...I'd love to see that!)