About all I can tell you is that I buy broccoli plants in a 6 pack and buy brussel sprouts plants as well. They are both slow growing and I am in west Michigan so I never have started them by seed. Always have a great broccoli crop. Brussel sprouts matured and had lots of little cabbages but the deer came through and stripped them. If it was dry where you are at could be not enough water. They both like cooler weather. I have almost no experience with cauliflower.
Thanks for the tip.