The late singer's manager Louis Walsh has vowed to give his friend - who died of natural causes aged 33 at his holiday home in Majorca, Spain, last weekend - "the best send-off ever" at the service, which is being carefully planned by his bandmates Ronan Keating, Shane Lynch, Keith Duffy and Mikey Graham.
Louis said: "In Ireland we've a tradition of funerals where we can be sad and happy. We'll give him the best send-off ever.
"The boys go to Majorca and bring him to Dublin. They'll stay with him all night. His mother said he would not to be alone.
"I think the boys are going to be in charge of everything. They're his best friends."
The group - who will carry Stephen's coffin along with two family members - are currently considering what to sing at the service, which will be attended by stars including Westlife, members of Take That, Sir Elton John and his partner David Furnish.
Family spokesperson Gerald Kean said: "We expect it to be a very musical affair in tribute to his talent."
A source close to the band added: "They know it's going to be the hardest thing they've ever done but this is their last chance to sing alongside Stephen.
"They're working on a tribute now."
Thousands of fans and well-wishers are expected to line the route from Stephen's home to the church, but have been asked not to bring flowers for the star.
Instead, Stephen's parents, Margaret and Martin, have asked for donations to be made to Caudwell Children - the charity Stephen was a goodwill ambassador for.
A spokesperson for the organisation said: "Stephen could never do enough for us."
Louis confirmed a memorial service is being planned in London, but admitted he, Boyzone, Stephen's husband Andy Cowles and the rest of his loved ones are "too upset" to focus on details yet.
He said: "The family are devastated. In a few weeks we'll have a celebration in London. Everyone is welcome to that but for now we are all still in shock."