To install an isolated network with WLAN and wired LAN is possible but you need at least an access point (AP) and a switch for it. Because you do not want an AP it is not possible to make what you want.
As seen from the comment you would like to have an access point devices can connect to and talk to each other. Some access points have also some (mostly four) built-in ethernet ports to plug in an ethernet cord. If this is enough then you have an integrated device for your needs. Purchase one. If you need more ethernet ports then buy an access point with only one ethernet port and an additional switch with number of ports you need.
If you want to save the money for purchasing an access point you can do it by yourself with the Raspberry Pi. @Jaromanda X has given a link to a tutorial in his comment. But then you have to do with router and AP you don't want to have.