In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
If your brother texted his wife three times I divorce you then that constitutes talaq-e-mugallazah (a permanently irrevocable divorce). They are no more husband and wife.
If they wish to be married again, the wife will have to follow the halalah procedure. That is she marries another person after her iddat passed. The new husband must consummate the marriage. If he divorces her, she may remarry her former husband after the expiry of her iddat.
The iddat is three menses if she is not conceived. If she is conceived the iddat is till she gives birth.
And Allah Ta’āla Knows Best
Mufti Ebrahim Desai
(Ustad/Teacher)