Learn Portuguese (Portugal): Eles são uns amigos novos.

Uns is the plural form of the masculine indefinite article um (a/an). While um means "a" or "one", the plural uns translates to "some". Because amigos (friends) is masculine and plural, the article must match it!

Could Eles refer to a group of women?

No. Eles is the masculine "they". It is used for a group of men, or a mixed group of men and women. If it were a group of only women, the sentence would start with Elas and the rest of the words would change to match the feminine: Elas são umas amigas novas.

Why is the word order amigos novos instead of novos amigos?

In Portuguese, adjectives (describing words like novos) usually come after the noun they describe (amigos). So instead of saying "new friends", the structure is more like "friends new".

Why do we use são (from the verb ser) instead of estão (from the verb estar)?

Both verbs mean "to be", but ser is used for permanent or defining characteristics. Being someone's friend is considered a core, lasting relationship, so we use são (they are) rather than estão, which is for temporary states like feelings or physical locations.