If there are only men or a mixture of men and women then it's "Eles estão felizes". If there are only women then it's "Elas estão felizes."
The correct way to say Happy Birthday to someone who speaks European Portuguese is as follows. Say "Feliz aniversario." That means Happy Birthday in Portuguese.
You say "feliz".
"Feliz dia da mãe."
"Happy Anniversary" in Portuguese is "Feliz Aniversario", the same as in Spanish.
You can say "Feliz aniversário de casamento" in Portuguese to mean happy wedding anniversary.
"Parabéns a você" is how one would say "Happy birthday to you" in Portuguese.
You can say "Estou muito feliz" in Brazilian Portuguese.
Feliz Aniversário
"feliz aniversário"
Feliz Sabado
Felizes Férias.
Feliz Aniversário!