Considering they're pets maybe:
Night and Noon
Nyx (night) and
Nishant (dawn) even though
Nyx is really feminine...
Nemo (nobody) and
Narendra (lord of men)
Nenad (unexpected) and
Naim (tranquil)
Nemanja (without possessions) and
Nail (attainer)
Navin or
Neo (both: new) and
Nestor (for its figurative meaning of old and wise)
Ninad (sound) and
Nirav (quiet)