I like both of those names, in all ways (in those sets, with "Zelesski," with Morgan Rae).
The only thing that I don't really care for is how Kay rhymes with Rae, but a pair of sisters might love having rhyming middles, so that isn't a drawback so much as a personal preference.
Also, do you plan to have a third? If so, and you have a Morgan Rae and a Molly Kay, these two names sort of set up a pattern (M-name with 2 syllables, rhyming middle). Patterns can be a double-edged sword. Stick with them and the names could start sounding kinda cheesy. But break from them and the set could sound discordant. (Also, no kid wants to be the odd one out.) Just food for thought.