Geschwister
siblings
A person's brothers and sisters taken together.
Ich habe zwei Geschwister, einen älteren Bruder und eine jüngere Schwester.
I have two siblings, an older brother and a younger sister.

siblings
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siblings
A person's brothers and sisters taken together.
Ich habe zwei Geschwister, einen älteren Bruder und eine jüngere Schwester.
I have two siblings, an older brother and a younger sister.

As with other words with the prefix 'Ge-' (e.g., Gebirge, Gepäck), 'Geschwister' (siblings) is a collective term. It groups together 'Schwestern' (sisters; historically used for all close relatives).
Meine Geschwister und ich verstehen uns sehr gut.
My siblings and I get along very well.
'Geschwister' (siblings) is a plural form that stands for brothers and sisters together. However, the word can also be used for a single person when you do not know the gender or it does not matter.
Hast du Geschwister? – Ja, eine Schwester.
Do you have siblings? – Yes, a sister.
The typical question is: 'Hast du Geschwister?' (Do you have siblings?). To state the number, you say, for example, 'Ich habe zwei Geschwister.' (I have two siblings.) or 'Wir sind drei Geschwister.' (There are three of us siblings.). The second phrasing includes the speaker in the count.
Wie viele Geschwister hast du?
How many siblings do you have?
brother
'der Bruder' and 'die Geschwister' both belong to the topic of family. 'Bruder' means one male person in this relationship. 'Geschwister' means brothers and sisters together and is normally used in the plural. Learners may confuse the words because a brother is also one of someone's siblings. If you mean a specific male person, you say 'Bruder'. If you are speaking generally about all of a person's brothers and sisters, you say 'Geschwister'.

Morgen helfen Lena ihre Geschwister beim Packen.
Tomorrow, Lena's siblings will help her pack.
Frau Klein fragt, ob Max seinen Bruder zum Training mitbringen darf.
Ms. Klein asks whether Max may bring his brother to training.