No you’d say “They are tall.” Because that’s how we conjugate that in English. They has always been used as both a singular and a plural because we don’t always know the gender of who were talking about. In French il/ils is the default when you don’t know a 3rd person’s gender. Il/ils is masculine.

It isn’t. I’m a French speaker, I’m telling you it isn’t. Vous is second person singular or plural. They is third person singular or plural. They is NEVER second person. Vous is NEVER third person. This is how the language is used around the world today.