I would say 1, 3 or 4 was a greater possibility than 2.
How to manage? IF there are no cavities for them to use as spawning sites, then just catch and remove every one you catch. If they are bullheads instead of catfish, then LMB in sufficient quantities will eat the YOY. You might never get them all out of the pond if they are BH.
I think you are correct 1 might be the most likely since he had to boys that were less than 18 when the pond was built.
I think I might bottle fish for the cats.
