I just bought a home with pre-existing fruit trees and grape vines(I'm completely new to this). One tree is apple and the other is unknown. I looked at the unknown tree today and there were tiny shiny flying insects( they look like overgrown gnats) landing all over the leaves and fruit, and the leaves are turning orange and brown, but the apple tree right next to it and the grape vines behind it are green and healthy looking. what's going on?

The photo attached is of the tree i am worried about. Also can anyone identify it?

It looks like cedar apple rust. Do you have a lot of cedar trees in the area? The fruiting bodies of the fungus that causes it look like a bright orange/yellow octopus on the cedar trees in rainy weather.

I'm not sure what kind of trees are around, It's a residential area though. Is this anything to worry about? Harmful to the tree?

It can defoliate the tree and cause some loss of growth because of the large areas that can't photosynthesize; also the apples can get spots that are orange and raised and unsightly, making them unmarketable (tho they're still edible). The infection is over at the end of the year and the tree can't catch it from itself - it has to catch it from a cedar tree and vise versa. See http://www.nysipm.cornell.edu/factsheets/treefruit/diseases/car/car.asp