If you lay out as situations - you have these situations:
Balance (just after extended rest):
Each sword is a +1 Magic Rapier (+1 attack, +1 damage, +1d6 on crit)
After one kill (and yes, non-minion):
Mainhand sword: +2 (+2 attack, +2 damage, +2d6 on crit)
Offhand sword: +0 (+0 attack, +0...