Complex sentence: Samau'al argued in his book that since the children of Esau are described in Deuteronomy 2:4-6 (and in Numbers 20:14 as well) as the brethren of the children of Israel, the children of Ishmael can also be described the same way.
Split into simpler sentences: Samau'al argued in his book that since the children of Esau are described in Deuteronomy 2:4-6 (and in Numbers 20:14 as well) as the brethren of the children of Israel. Thus, the children of Ishmael can also be described the same way.