The older son of John Frederick II , and John Ernest ( d 1638 heirless ) , the younger son of John Frederick II , received together the territory of Saxe-Coburg-Eisenach . John Casimir ( d 1633 heirless ) , the older son of John Frederick II , and John Ernest ( d 1638 heirless ) , the younger son of John Frederick II , received together the territory of Saxe-Coburg-Eisenach , but got a legal guardian because they were underage .