Is the expression 'ex aequo' used in proper English?

No. It’s a Latin term, but I think it’s only used commonly in French. It’s not even listed in the OED. You could say they are in joint first place, or joint winners in English, I’ve also seen co-winners used, but again it’s not in the OED. read more

Mais en cas d'égalité parfaite, il n'y a pas de tirage au sort : les deux finalistes seront déclarés vainqueurs ex aequo. Le Monde (1999) Première avec dix points d'avance, mademoiselle Béatrice Vidal, deuxièmes ex aequo, mesdames.. read more

Read a lot of books written in English by native English speakers. Listen to English as spoken by news reporters from America. Try to be very aware of what you are saying, and speak clearly and precisely so that the words you are trying to say are the proper words for the situation. read more