Brothers Billy and Geoffrey Midmore, from London, were detained in Gillingham, Kent. A 33-year-old woman was also arrested.
Carla Whitlock, 37, was attacked in Guildhall Square, Southampton, on 18 September.
She suffered burns to her neck and arms and said she feared she would "lose the sight in her right eye".
She added: "It has changed my life completely. I'm coping with it as best as I can."
The mother-of-six was attacked outside the Turtle Bay bar and restaurant in Southampton's Guildhall Square.
The arrests followed a joint operation by police in Hampshire and Kent.
Police have made three arrests in connection with an assault in which a woman had acid thrown in her face.