Here are pictures...

Here is a link that might be useful: Pictures of slope

Anything aggressive enough to stop poison ivy that can survive in the understory and produce food all with little maintenance is probably going to get at least 8 feet tall, if you are willing to battle the PI until it is gone then there are a wide variety of low growing berries that would be wonderful under those trees.

How low do the plants have to be before you can see to the pond? In any case aggressive vines like PI aren't easily beaten and dealing with it your self will be more fruitful than trying to get a plant that will fight your battle for you.

I think 5 foot high will be OK if we have a "neat" appearance as opposed to scrubby jungle appearance.

Do you really want something edible? Or something that looks nice and can survive the shade.

There are lots of great edible options, but they are shrubs--witch hazel, spicebush, blueberries, juneberry, currants.

There are some low growing blueberries, you might try them, and sweetfern, although it needs dappled sun, but since PI loves that too, it seems like you might have that.

Understory plants--sweet woodruff (can be dried to make pot pourri, smells like vanilla), things in the mint family, mayapples (supposedly edible when ripe, they taste like soap to me), wild ginger (pretty dang spicy!), bear berry/knickknick, lingonberries, wintergreen, violets, fiddlehead ferns, touch-me-not/jewelweed (can use leaves for salve to alleviate PI).

Pretty ones--forget-me-nots. Those may be poisonous though. Jacob's ladder, and monkshood, which is DEFINATELY poisonous, but pretty. Turtlehead, gentian, other types of ferns.

Those are some I can think of for starters.