Niankhkhnum and Khnumhotep were "prophets of Ra" in the sun temple of Neussere, the 6th king of Dynasty V.
See:
- Mastaba of Khnumhotep and Niankhkhnum, Osirisnet, https://www.osirisnet.net/mastabas/niankhkhnoum_khnoumhotep/e_niankhkhnum_khnumhotep_01.htm