At 1st level, you learn one necromancy cantrip of your choice from any spell list. When you cast a necromancy cantrip that normally targets only one creature, the spell can instead target two creatures within range and within 5 feet of each other.
When you Cast a Spell that Targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip). To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level. For example, Magic Missile and Scorching Ray aren’t eligible, but Ray of Frost is.
My reading of this says that Reaper is an effect that happens to the cantrip the same as Twinned spell. So both would happen simultaneously, which circumvents the Twinned spell stipulation that it can only effect one target.