airport express and ethernet connection

This question may have been answered several times, but despite looking in different forums, I did not find a solution. Any help would be most welcome.

I have set up a network where an Airport express (n) is connected to a modem/router via ethernet. This works fine.

I want to use another Airport express (n) to connect a mac mini I use as server. The connection between the two bases is wireless, However, as the mac mini is only (g), I want to use the (n) capacity of the airport express by connecting it directly via ethernet to the server. This does not work

Thirdly, I want to do the same using an airport extreme (n) to connect 2 printers and an older Imac which airport is only (g) compatible. The base is connected to the emitting one wirelessly and the printers and the iMac are connected via USB and ethernet. the connection with the printer works throughout the network, but not for the iMac

The settings of the emitting airport express are "create a wireless network", "connect using ethernet", "allow this network to be extended" and "automatic channel".

The settings of the receiving airport express are "join a wireless network, Connect using wireless network", allow ethernet clients" and "automatic channel"

The settings for the receiving Airport extreme are "extend a wireless network", "allow wireless clients", "automatic channel" - the option join a wireless network does not exist.

Thanks in advance to all thse who will spend some time trying to provide an answer.