Aîne

Elle est l'aînée des filles.
She is the eldest girl. OR She is the eldest daughter.

Il est mon aîné de trois ans.
He is ...

Fils aîné.
Elder son OR Eldest son.

Fils benjamin.
Youngest child.

Ces jumeaux sont leurs premiers-nés
I am clueless with this sentence. What is jumeaux?

Leur fille aînée
Their eldest daughter.

Il est l'aîné de cinq enfants.
He is the eldest of the five children.

I copied the above French sentences from an online dictionary.
I tried to translate into English.
Please help me.