Yes, it is possible to belong to multiple Method Grid accounts.
Every account is assigned (by the Founding Architect) an account name. Once logged in, you will note that the prefix on your url (look at your browser address bar) is this account name.
Typically, Method Grid members will use different email addresses for their multiple accounts but not necessarily so. If you use the same email address for multiple accounts, we would recommend different passwords (just good practice not to use the same). At login, Method Grid then detects the email-password combination to send you to the right account. If you do use identical email-password combinations for multiple accounts, you will be presented with your account options once through initial login.