Well, there's Kelan, Anglicised form of Irish Gaelic Caolán, male and from the Gaelic word caol meaning 'slender'. How do you get from 'slender' to 'warrior princess' without being on a catwalk? Hmmm....could it be that someone out there has decided to 'feminise' what was never feminine and turn male name Kelly into Kellan? Is it possible that this same person found somewhere that Kelly supposedly means 'warrior' and since 'warrioress' isn't girly or cute enough tacked 'princess' on the end? They're wrong. It's from surname O'Ceallagh which means 'strife, war' and 'warlike' but not 'warrior'. Mike Tyson is 'warlike' but never ranked higher than 'fighter'. Most of WWI and II were fought by 'warriors' who were anything but 'warlike' in personality. And Kellan, whether from Kelan or Kelly, is still male.
Renny - where to begin. First I'll drop some Irish on you: there's rinn which means 'point', there's reannag which means 'star', rean which means 'arrangement' but 'small' is 'beag' - do you see beag in Renny? Me either. Wonder why that is...But I do know where you've been hanging out and finding these and can issue a general warning that they don't have a clue what they're talking about so take everything you read there with a grain of salt. Other more 'serious' sites list Renny as an Anglo form of Rathnait ('favour, prosperty') which makes mild sense (it's actually Ronit in Anglo form) but the etymology is deeply suspect. Renny has occurred in Ireland as a version of the French male name Rene. There are also towns called Renny - Lower and Upper and it exists as a surname, though that often seems to have been imported from Scotland and Northern England where Renny developed from Reynold. The man responsible for funding the Royal College of Surgeons in Ireland was George Renny...a Scotsman. At any rate, nothing to do with small or powerful and definitely not female.