Hundreds of people are standing outside St Peter and Paul's Church to say goodbye to the McSweeney siblings.
Grace and Luke McSweeney tragically died on Friday in a single vehicle collision in Clonmel.
The local community joined friends and family as a pair of hearses delivered the coffins to the church for the funeral mass of 11.30am.
The readings will be read by Jack and Aidan Phelan.
In his introduction, Father Billy Meehan said, "We are here conscious of separation, yet confident we shall meet again.
We are here to pay tribute to all Luke and Grace meant to us, and to remind ourselves of all they mean to God."
Video footage: Faye Dorgan
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