Those skeletons were not Owen and Beru. Both were a lot more formidable than their preferred modest lifestyle would indicate. They eliminated the first two Stormtroopers to arrive and stole their armor. Owen burned the bodies, and Beru sent a phony report saying they had interrogated and killed two civilians, but found no droids. Owen had already overheard Leia’s message and deduced Obi-Wan would be taking Luke to Alderaan, so they planned on reuniting there, but lost track of them when the planet was destroyed.