Los muchachos tienen problemas
You say, "gemelos."
las sucesiones
You can say los chicos for the boys, and las chicas for the girls.
Nothing, that's in English. But if you meant to say HOW to say teenage boys, then its "adolescentes"
hola chicos
Nuestros muchachos. (Chicos, niños.)
Odio los chicos.
girls, debriefia and boys, debriefio
acelerado for boys and acelerada for girls
me gustan los chicos
Los muchachos tienen problemas
Girl who are friends are amigas in spanish. Further boys are amigos