Have you actually looked into the sump pit? If the water is coming in that fast then you have some serious foundation problems and some serious ground water problems! If you have three major cracks that you know about you might have more you don’t know about.
In a house only eight months old you shouldn’t have ANY cracks! Is your house on old landfill or sand? I can’t believe it has settled that fast and that badly!
I would suggest getting an inspection by someone other than your warranty people first to find out what’s going on. It will probably cost you some money, but not nearly as much as having your basement flood.
As for the builder’s warranty they generally have more holes than a bowl of Cheerios. Hopefully your warranty is worth the paper it’s written on.
The ground around the house might not be sloped properly, but your main issue is still the cracking that shouldn’t be happening already.