Before we get started, it's important to note that most conifers are more or less edible, (some taste better than others, though!) with the exception of the yew tree family. It's highly toxic to humans and should be avoided.
Doug fir is not a fir tree, but its own genus entirely. Their needles grow all the way around the branch, and the buds at the end are brown and cone shaped. Doug fir cones have a characteristic “mouse tail.”
Hemlocks have short flat needles with 2 white lines on the underside. The needles can be different lengths on the same branch. In the spring, they produce bright green fresh tips. Hemlock cones hang downward and vary in size.
Junipers have needle or scale like leaves, depending on the species. Some, when young, turn to scales as they mature. They have a distinctive aromatic “gin-like” fragrance and produce blue seed cones known as juniper berries.