Welcome to the forum, have you thought about aeration. The reason there is no fish could be fish kills are likely in that size/depth of pond in your area.
By adding aeration you can help with that and increase the fish carrying capacity.
If your willing to deal with kills and re stock every so often you could try without. Not going to be a large investment in terms of stocking cost .
With aeration I would go with HBG 40-50 , YP 15-20, HSB 5 , you could also feed these fish pellets which is fun as well. Boys might enjoy that as much as fishing .
If no aeration you might just want to experiment with smaller qty's to see how they do.
