Your right it doesn't really apply, he was introduced well after the colony was established.
There for he's clearly not actually a parent of any fry.
Getting back on track, I have had Fry grow into adult hood and chase the father out of the tank (found him the next day all dried up).
As to why yours chase their fry I have only one thought: Possibly, new parent syndrome.
I"ve seen a few times with angel fish and N. pulcher , they'll just eat their first few batches and eventually stop.
Have you had your Multies for long?