I'd call them something else, as there's already an official card "Spice Merchant", which would cause confusion since it's not a "Merchant" card even though the name conforms with this set. You don't need "when you play this" if it's just an effect that happens when you play it; "you may play another Merchant card from your hand" is fine.
Actually your wording is problematic because "when you play this" effects trigger before the card resolves (for example, "when another player plays an Attack card" such as Witch, you reveal a Moat before they get their +2 Cards and give each other player a Curse). In that case, if I play Apple Merchant, actually I have to play my Pear Merchant for +1 Card, +1 Action before I get my +2 Cards from Apple Merchant. This matters because, as you have it now, I can't play the Pear Merchant that I drew by playing Apple Merchant. That's unintuitive, and probably unintentional. (If it was intentional, you could just put the "you may play..." before the +2 Cards.)