I would breed the son back to mom and see what happens. If you don't get something cool, then try the daughter to the father. The only reason I suggest the son to mom first is because he'll be ready to breeed sooner than his sister and you might get some answers, or at least an idea, sooner rather than later. But the ideal pairing, imo in this case, would be the daughter to father. So if you don't mind waiting for her to grow up (3-4 years), then just wait and put the father to his daughter for, hopefully, some real results.
BTW, if you DO do that daughter x father pairing and get some more amazing purple animals, I would like to be on the list to get one.....![]()