Okay, sorry for my missinterpreting of the situation any many thanks for the detailes explaination.
Thanks to you, really, you are helping me in something I really wanted to accmplish and had no clue to what I have been doing wrong... I didn't know who could have helped me and many thanks to you trying to do so...
Some routers do weird stuff when not connected to the internet. Most of the time it's just a settings, so when you look for firewall settings also have an eye for anything labeled like "don't rely on WAN", "local DHCP without WAN" or anything sounding even remotely like that (but make a backup of the router settings before playing with such options).
Ok as long as I manage to enter the router config page I should be able to find this kind of option, of course the router should have the option to reset to default values in case something goes wrong... But first task: enter the router via browser even if it's not the main router with internet...
Is your routers DHCP server even configured to handle out 192.168.1 with 255.255.255.0 netmask or was that a wrong DHCP attempt, too?
This is something vaguey obscure to me, is there also here an option inside to check and adjust it? What is the configuration parameter referring to handle 198.168 type IPs?
For debugging purposes it might be a good idea to connect the PC to the isolated network (but not to the PCs main network where it gets internet access from as Windows PCs are... Well... Not really good az handling multiple connections). Why this might be a good idea? Well, you could for example check if Wii U and 3DS are pingable or if the whole LAN is f*cked up. Also you're able to check for problems way more simple (like what I said before: Output of ipconfig. There are way more things to check that way, like routing tables and stuff... But one step after the other, right?)
Ok I will try to connect the PC to that LAN to make some test, even losing internet for a while I could check if the LAN works, I assumed it did since 3DS and Wii U received response and an IP but I actually don't know... I don't know how to make a ping test on a device sharing the network but I could easily find out how to probably...
I will post some test results after I will be back online after the tests...
No, no and no. This is not the time to think about improving performane. You can't tune something that doesn't work at all...
I was planning ahead, I know that even when it will eventually work it may be not perfectly fluid, so I could try improvements and I'm trusty that we will somehow manage to make it work!