The first disciples came together for worship, fellowship, and prayer (see also 2:42, 46–47; 4:24–31; 5:12; 12:5; 13:1–3). The faithful women who witnessed Jesus's crucifixion and resurrection were there (Luke 23:49, 54–56; 24:1–10, 22).
The brothers of Jesus did not believe in him during his earthly ministry (John 7:3–5; compare Matthew 12:46–49). But they became his disciples after his resurrection.