I’ve never bred the elephant ears but they should be very easy to breed just like other guppies provided good care and that the fish you purchase are of high quality. As far as the number of fry I’d expect around 30 but guppies can give birth to as many as 200 so prepare for more. As far as I can figure out it seems that the big ear gene should be in most if not all of the fry.
I'm still breeding them. As already mentioned above, they're not hard to breed. But the number of fry from each batch do differ from female to female. In my experience, females have a good grow potential. A good fullgrown female has a ferm build and will be able to have an average number of fry of 20-40. Overhere, newborn fry aren't that small. But it also depends on the quality of the bloodline you're working with.
Can we maintain the size of the big "ears" in breeding. Someone told that he didn't get the big ears on all of its offspring. Only some of the offspring got that characteristic of the parents. Did you experienced any problem like that? Are you doing inbreeding or cross breeding?
It's true that not all offspring do qualify being big ears phenotypically. But the majority will be phenotypically big ears. I only use inbreeding when a specific characteristic needs improvement. Inbreeding in the first couple of generations isn't a problem. No deformaties will show up that fast. I myself like to purchase new bloodlines to add to my current group on a regular bases.
You can also let related offspring grow up seperately and let them become seperate lines for a while. Later generations of specimens of those seperated groups can be mixed up with the other groups again. Also in that way, deformaties won't show up that fast. And specific characteristics within that line can be ensured.