Connection via MAC should work, but try settings your PC to static with an IP address in the 192.168.88.0/24 range.
It could be an issue with Winbox 4, you could try (good ol') v3.x but you will need some trickery with WINE as v3 Is Windows only, see:
But if you set your PC Ip/network correctly you can also try SSH or Webfig (just point your browser to 192.168.88.2, but try also the other device 192.168.88.3).
In any case I would connect your PC directly to one of the devices, so that any possible issues with your existing network are ruled out.
And yes, if you have only one device connected via ethernet but you see both the .2 and .3 It means that the wireless connection Is established.