Yrartz !: Do not be alarmed!

Vicious, man-eating aliens land undetected during a natural event. Brothers Bob and Tom are the first to discover them and live to tell about it. They try to warn the town before it's too late. The invaders surround the village and begin eating everyone they encounter. The towns people organize a defense.
Brother and sister, Nathan and Kelly, join their friends, Bob and Tom in the fight. Later they are sent on a mission. The four get cut off from town. They are chased thru forests and swamp. They finally make their last stand at Grannies farm.