my brother play spiral knights on steam and want to interact with the wiki and forum on his owe account but using the steam on the site is... complicated so he wants to know if he makes an account on the website and merges it with steam will he regert doing so and which one would he have to log into to make it work?
First, any player can have multiple accounts. You can have a Steam account for actual playing, and a web site account for wiki editing that you never play on. Even people like me who have all of their accounts through the web site have to log into the forums and wiki separately from playing the game. So using two accounts in this way does not require any extra work.
If you like, you can then convert your web site account to Steam. But at that point it's a Steam account, so it probably isn't able to edit the wiki anymore. This is a guess; I don't use Steam. So my suggestion is not to convert that account to Steam.
If I'm wrong, someone will correct me.