Question about ips and forum boards

Here and in the most of the forum boards, double accounts are not allowed.
I think that the mods know which accounts are from the same member from the ip (same ip, 2 nicknames posting).
But in some cases, two people have the same ip. For example me and my brother we’re connected to the same router. That means that our accounts (tolis_01 and kostas07) have the same ip (sometimes we even use the same pc).
How can the mods know which case is double accounting and which not?
There isn’t any danger of us getting banned, is there?
Answer #1
It depends who sees it.