What distinguishes لَمْ يَفْعَلْنَ from لَمْ تَفْعَلْنَ?

Negating the Imperfect with Lan and Lam: Subjunctive, Jussive and Full Paradigms

• The first is active, the second passive
• The first is past negative, the second future negative
• Third-person feminine plural versus second-person feminine plural
• Singular versus dual