If a devisee who is a grandparent or a lineal descendant of a grandparent of the testator is dead at the time of execution of the will, fails to survive the testator, or is treated as if he predeceased the testator, the issue of the deceased devisee who survive the testator by five days take in place of the deceased devisee and if they are all of the same degree of kinship to the devisee they take equally, but if of unequal degree then those of more remote degree take by representation. One who would have been a devisee under a class gift if he had survived the testator is treated as a devisee for purposes of this section whether his death occurred before or after the execution of the will.