You will know that all the offspring will be blizzard. You will also know they are het for eclipse and Murphy's patternless. You will have no idea if they are het for Tremper Albino unless you prove them to be.
They can be proven by breeding them to a pure tremper - if there are albinos then the gecko is het, if no albinos you can be relatively sure that it is not het. However, there's always a small chance you are just super unlucky and didn't get an albino when the gene is there. The more non-albinos produced the smaller the chance.
The only way to get a banana blizzard in a single year of breeding would be to purchase two banana blizzards or purchase one banana blizzard and one het for all the banana blizzard traits.