Well, just a little update: the batch was no good. Nothing hatched, so we cleaned out the pond and tried again a few days later with 2 different females and 3 males. And this time we are in luck!
Hatching happened after 4 days, and they are 3 days old now. After a little counting we came up with an number anywhere between 1247 and 2079 - sorry, there are just too many to count.

And when we think we have figured out where they all are, then somebody moves the spawning mob that is still in there, and it just keeps moving full of fish. So, now we are proud parents after all, and the feeding is just plain crazy. But they are so cute, and I try to get a picture of them. They actually come out pretty good with the blackness of the pond bottom as background. Their tummy is either green (from the algae on the walls) or pinkish from the daphnia/brine shrimp.
I give them daily water changes with a very weak fountain pump, and they do fairly well. So small, and yet already able to swim away from the suction like nothing is going on. Pretty strong, those little stick things.