Which statement correctly explains the aspect “Restrictive force of innamā” in the example “إِنَّمَا الْمُؤْمِنُونَ إِخْوَةٌ”?

Qasr by Coordination, Negation–Exception, and Innamā

• Coordination versus innamā — Zayd is a poet, not a writer / Zayd is only a poet.
• Coordination and qasr al-ifrād — Zayd is a poet, not a writer.
• Alternatives in coordination — Zayd is a poet, not a writer.
• Restrictive force of innamā — The believers are but brothers.