Short answers, pulled from the story.
The earliest certain reference to the Ogdoad appears during the reign of Hatshepsut. This specific moment is marked by a dedicatory inscription carved at the Speos Artemidos during the Eighteenth Dynasty.
Nu and Naunet form one pair while Heh and Hehuet make another. Kek and Kauket stand as a third couple, and Amun and Amunet complete the fourth group.
Nu and Naunet represent the primordial waters that existed before creation according to hieroglyphic texts. Determiners for sky and water accompany their names in these written sources.
Temple reliefs from the Ptolemaic Kingdom depict males with frog heads and females with serpent heads. These physical forms distinguish them clearly from other deities worshipped across ancient Egypt.
Modern scholars like Harco Willems have assigned ontological concepts to the four pairs because Budge postulated that ancient Egyptians had no very clear idea regarding specific functions for each pair. No obvious way exists to allot four distinct functions to the four pairs according to available texts.