Choose the right description for the following people, be careful with the adjective agreement: your brother and sister (2 points) elles sont adorable. elles sont bêtes. ils sont égoïstes. ils sont supers.

The answer is Ils sont égoïstes because the rule is:
"The French pronouns ils and elles. Ils is the plural equivalent of il singular. It means they, when they refers to all masculine subjects, or a mix of feminine and masculine subjects."

Hi !

your brother and sister = masculine and feminine
as with nous or vous, if there are a man and a woman , the masculine takes over the feminine.

Julie and I (being a boy) = nous sommes partis (P;composé) not "parties"
pierre et Julie = vous êtes beaux (not belles)

so brother and sister = Ils (plural but masculine)

Ils sont égoïstes (they are selfish)

Ils sont adorable = Ils sont adorables
Elles sont bêtes = Ils sont bêtes
Ils sont supers = Ils sont super

for the last one , super is an adverb, so   unchangeable, invariable.  However, sometimes you'll see written "Ils sont supers" in some everyday magazines But according to the correct grammar , it stays an adverb

Is this french and is mary melons treatment on the island a book ?

On a daily basis you have the opportunity to read french on products used in the united states look at the list products which is most likely to have french on it :
- hair products