What do you learn about Joel and Malthace in the first chapter of The Bronze Bow?

Joel and Malthace are presented to the reader through the eyes of Daniel. Even before he is able to identify them, he observes that they must be siblings:

Brother and sister, that was evident. They moved alike, with a sort of free, swinging ease. They had the same high cheekbones and dark ruddy complexions. Their voices were sharp in the clean air.

Afterward, when Daniel hears the girl call his brother by name, he recognizes the boy as Joel Bar Hezron, a boy he used to go to synagogue school with and who had a twin sister called Malthace. Without being told so, the reader then guesses that the girl with Joel must be his twin sister Malthace. It appears that the two are extremely fond of each other and that they love the land of their people, for they dare to climb the dangerous mountain all by themselves just to admire various things in the valley below. When the brother and sister see Daniel, they do not run away even though Daniel looks rugged and wild. Instead, the boy “clenches his fist,” and Daniel knows that he is no coward; he is ready to defend himself and his sister should the need arise. Joel and Malthace are kindhearted youths, for they talk to David, freely giving him all the information they have about his loved ones back in the valley. They even share their lunch with David.
Further on in the chapter, the reader learns that Joel shares David’s disdain for the Romans. The twins are patriots and dream of the day when their people will be delivered, by the Messiah, from Roman rule.