Their native language was ancient Egyptian, a member of the Afroasiatic family, which also includes the Semitic languages. Ancient Egyptian had five phases (Old Egyptian, Middle Egyptian, Late Egyptian, Demotic, and Coptic) and four main scripts (hieroglyphs, hieratic, Demotic, and the Coptic alphabet).

I wrote about the ancient Egyptian language in How advanced were Bronze-Age languages? and How much did hieroglyphics change over time?