The dynasty which united Kush and Egypt after the end of the New Kingdom was A) Nubian dynasty.
Because of Nubian dynasty, Lower Egypt, Upper Egypt and Kush (Nubia) were reunified and all together created the largest Egyptian Empire since the New Kingdom collapse.
This dynasty was the 25th and began with the invasion of Upper Egypt and ended up in a war of several years against the Assyrians; which finally caused the destruction of the Kush-ite Empire.