The written form stays the same; the pronoun tells you who acts.
● هُمَا تَكْتُبَانِ — Those two women write.
● أَنْتُمَا تَكْتُبَانِ — You two write. This can address two men or two women.
Therefore تَفْعَلَانِ alone does not identify one unique slot. Read the pronoun or the surrounding sentence before translating.