Final answer:
The praying figures in the lunette of the Catacomb of Sts. Peter and Marcellinus are likely a commemoration of a family burial tied to the Christian belief in personal salvation.
Step-by-step explanation:
The placement of a man, a woman, and at least one child in the praying position found in the lunette of the Catacomb of Sts. Peter and Marcellinus can be best explained as a commemoration of a family burial. Early Christians who converted from traditional Roman beliefs brought with them the cultural value of images and desired similar practices in their burial traditions. The transition from cremation to inhumation led to the creation of catacombs and sarcophagi which became adorned with religious artwork that often depicted salvation narratives. Given the tradition of burying family members together and the Christian emphasis on salvation, the praying figures in the lunette likely represent a family hoping for the salvation of their deceased relatives.