Guild Wars 2

It says in the wiki that you can be a member of up to 5 guilds on one account. Can someone actually create two guilds and be a member of three other guilds, that were created by three other accounts?

Indeed they can. However, you can only represent one guild at a time. You will only see the guild chat of the guild you represent, and only be able to use their upgrades, not any other guilds. In addition, only the guild you represent will gain influence from your actions, with influence being needed for guild upgrades. Thus, some guilds will require repping.