The names of the three nations represent the people of those nations. AT: "the Israelites will be the third with the Egyptians and Assyrians" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Possible meanings are 1) "join together with" or 2) "be the third blessing with" or 3) "be equal to." (See: [[rc://en/ta/man/translate/translate-ordinal]])