How to configure to checkouts

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My store has 2 checkouts.  I will need to setup client mode because my modem is not close to my retail checkouts so I will attach an Apple Airport Express to my modem, and then I know I will need two more (one for each receipt printer).  My question is will the 2 Airports that are connected to the receipt printers both be able to "talk" to the Airport that's attached to the modem, or do they each need their own Airport attached to the modem, meaning I need a total of 4?  These things are not cheap!  And I'm confused.