Ah, was crying with laughter at the Balonz thread, until the truth was revealed, then it just went a bit flat.
That scenario was amusing in its initial sense, because it's a contemplation about a silly name. It's suddenly not so funny when it's a real life child's name, and all the ramifications it will hold. The disbelief, people trying to hide their reaction, and thinking they are joking, every time the poor child introduces himself. The PP who've asked their children their opinions, and they've replied, "they'll get bullied." The fact they've even got the Cloud middle name wrong by their reasoning, as the silver lining is the happy part around the miserable cloud in that saying. I don't think "hippy free spirit" I think Kardashian/Towie wannabe.
It's really hard I can imagine OP, as basically, you have no choice in the matter, but you can see the bigger picture, whilst DS and his partner are so proud of their thought up name and wonderful story behind it. Stormy is about your only option, which is recently newly famous as the Jenner baby and the porn star Donald Trump has been in the news with. You'll mainly get the Jenner (Stormi although it's identical in sound, and I think a baby girl) association.
I'm racking my brains what you could nickname Stormy-Water as, that the mum and dad would think you were simply shortening, as Stormy-Water is a mouthful regardless of anything else. No different to something long like Mariella-Anna, that you'd shortened to Elle. It's just such a tricky thing to shorten to anything decent, or that doesn't sound like you're saying something weird solely to avoid the full name.
Tor? Sorry, that's no better is it. How do you feel about Storm?