Family friend and long-time campaigner Angela Fredericks said there had been four immigration ministers since Priya, Nades and their daughters were taken from their home in Central Queensland more than 1000 days ago.
She said it was now up to the Prime Minister to "make the captain's call" and let them come home.
"Mr Morrison has always had the power to instruct his ministers to let Priya and her family return to Biloela, but he has let little Kopika and Tharnicaa live the majority of their lives in detention," she said.
"Today, we ask Prime Minister Morrison to show some compassion. Let them come home to Bilo."
Friends will gather at 5am on Friday in Biloela to mark the time the family's home was raided, before supporters in cities and towns around Australian gather at dusk.
Australian actor and former Biloela resident Michael Caton will speak at the Sydney vigil, as will Senator Kristina Keneally.
Life in detention is "getting harder and harder" for the family, according to Ms Fredericks, who is in regular contact.
"Little Kopika, she's getting more and more distressed by the situation," she said.
"She loves going to school and loves getting to leave the detention centre, however she's just so sad about having to constantly go back there and be locked up."
For three-year-old Tharnicaa, detention is all she's known.
"For her its normality, which is really sad," Ms Fredericks said.
The family and their lawyers have been involved in a protracted court battle based on Tharnicaa's right to apply for a protection visa.
Last month the full bench of the Federal Court rejected an appeal by the federal government over an earlier ruling by Justice Mark Mochinsky, which found Tharnicaa was denied procedural fairness in making a protection visa application.
Ms Fredericks said the court process showed "the inadequacies of Australia's immigration system".
"A court can judge that fair procedure hasn't been made, and yet the courts still actually have no power to make any calls on the case, it all still comes down to an individual bureaucrat making the (visa) decision," she said.