[Van down by the river]

Samw is correct any two are a pair. makes being a matchmaker easy huh?

What's the difference?
Distribution.
Lysmata grabhami - with solid lines on the tail is the Atlantic species

Lysmata amboinensis- has white patches on the tail and is Indo Pacific to Red sea.
Chances are more of you have L.amboinensis as a larger portion of shipments are Indo Pacific than Caribean.

As far as the Peppermint shrimp goes I found 6 very similiar species that all could be labeled as Peppermint shrimps.