If eels can get into your pond, sounds like you have a stream that is at least connected to your pond at times. This means, fish other than ones you stocked may be able to migrate in to your pond at times of high water. Often times, people who are not familiar with sunfish misidentify them as BG when they may be other species. When it warms up, I would catch a few of your sunfish and post pictures of them for identification. I would also start to document the relative weight of your bass. With a little more information, we can give you better advice. Until then, I'd hate to give advice that may be inaccurate.
Some other info I'd like to know:
How deep if the pond?
Is it aerated?
Does anyone feed the fish?
How cooperative are the other owners of the pond?
Sounds like you have a possible gem on your hands. I think your kids will grow up loving the pond. I grew up with several ponds in my neighborhood as a kid and spent many hours staying out of trouble fishing them and learning about nature.
