wierd little problem i have

[nytro]

i came here to see if anyone could help me or tell me what's wrong:

whenever i see my brother using Graal on his computer, I can't see his text or where he moves on the screen, and vice versa.

we have 3 computers, mine, my dad's, and my brother's. the LAN and DSLmodem are located on my dad's computer. through my dad's computer runs the LAN which carries the DSL internet to the other 2 computers so that they may have the internet as well. now if me and my brother on our own computers run Graal, it works fine, but if we see each other, we can't talk to another or see where the other walks on the screen.

i think it's a problem with the isp and such, but i wanted to ask someone who knows of anything like it and if we can fix it. thanks.