The Church gives priority to the singing of the Order of Mass – the Alleluia, the Holy, and Great Amen, for example, and the songs proper to the Funeral Rite, for example, the Song of Farewell. The priest will be able to discuss which version of these will be most fitting.
Music at a Funeral Liturgy should always be drawn from the broad repertoire of Christian hymns and compositions. A piece of music from another source may be used after the formal Liturgy has finished provided there is nothing in it inconsistent with the sacred nature of the place and the occasion.
In considering what to sing, do take into account the likely congregation and how they will respond to the invitation to sing. If the congregation is small, or unfamiliar with singing, it may be better to rely more on the organ or other instrumental music than song only.