Okay I just thought of this.. I have never been apart of a breeder loan but if I were to be in your position I would do something like this. Breed the animals, and if/when she lays eggs you two will grab a marker and mark your eggs. You alternate until all the eggs are marked. Separate each group of eggs and whatever hatches, hatches. Luck of the draw. Seems fair to me? Maybe not the most professional.. But still..