On a ranch I used to own I found very similar conditions that you have described. The solution recommended to me was to stock breeding sized copper nosed bluegills fairly heavily. Since they compete with the Green sunfish for territory and spawn four times a year they croud out the green sunfish. Also spend some time fishing with small spinners for the greenies. They are very aggressive and are easy to catch. You can thin them out this way. Last, be sure you have plenty of bass to eat the greenies, stock mature fish if you have to. I did. After two years, the green sunfish were severly reduced, the coppernosed had established themselves and prospered, (be sure to fertilize the lake and feed protien) and the bass population both in size and numbers flourshed. There is usually a positive solution to most problems. Remember too, this is fun stuff so make your remidies fun. Hope this helps. B