Yes but the English translation shouldn't be translated as if it is Spanish. It is my uncle should be accepted in English. You just have to keep in mind that the way the Spanish hear the Spanish sentence is different. So i still don't get why they didn't allow 'it's my uncle'.
"Es mi hermana." "Es mi hermano." "Es mi madre." "Es mi perro." It's not that "es can mean he" but in Spanish you don't say "IT is my..." and then refer to a human, so even though we do sometimes do that in English, DuoLingo expects us to play it safe and use the English translation that is closest to the way it is understood in Spanish. I guess.