2 steam accounts, 2 computers, 1 internet (router)

[Kaloren]

Can I play in game online (multiplayer) with my brother on 2 different steam accounts, two different keys to game, 2 different computers but the same Internet, computers are connected to the same router. It is possible without getting ban or block or something like that?

[TirithRR]

Yes, you can do this.

My brother and I do it all the time. He has his computer and Steam account, I have my computer and Steam account, and we both use the same internet connection.

[spoof]

in some games and for some routers you need to set a clientport.
https://support.steampowered.com/kb_article.php?ref=6370-QPHJ-3567&l=english

[Kargor]

Yes, it basically depends on the game and how exactly it implements the multiplayer.

Anything that just connects to an actual server (as opposed to one of the PCs participating in the game) should work without any adjustments (barring overly restrictive router or firewall settings, as usual).

Multiple connectiions from the same IP address should not cause any problems nowadays, as it's a very common occurrence and any server that can't deal with that because it uses an IP address to identify connections should be considered broken.

Games that use one of the participating PCs as hosts may or may not require port forwarding on the router, again depending on how it is done. In particular, games with a specific LAN mode won't even go through the actual internet...