Hi,
I've already connected the six other PCs via their IP-address. The problem is that the other four computers are connected to the network via another router/ access point. This puts them in another IP-address range (192.168.x.x) while all other computer are on the 10.18.x.x range. I've already tried to ping them but that doesn't work.
I think a little setting inside the router is prohibiting this connection but I can't find out which one. If I could I would just use a switch instead of router/ access point but my IT-department can't give me this because the access point is essential for other teachers their classroom.