Japanese Maples, Acer palmatum, are susceptible to frost damage, especially at the northernmost limits of their range. Obviously native to the Orient, Japanese Maples do best in your area when in a semi-shaded location where they are protected from north winds. I too am in zone 8 and have a neighbor who cares for her Japanese Maple with all the love that she showers on her six-year old grandson! Treated as containerized pets, her Japanese Maples get lots of TLC with snuggly blankets when freezes threaten. It seems to help.
Check with a local nursery to see if your variety is suited to your area; they may have some good advice for you. It is possible that your trees are poster children for the saying: Wrong Plant, Wrong Place. In that case you may wish to move your plants to a better location. Or you may wish to replace your trees with native trees that will not be a bother, such as a Plum or a Dogwood. Good luck!