Yes, you can have more than one login page.
The key thing to make sure of is that each login page is setting the same session variables using the same names. In the Authenticate User Server behavior, on the third step of the wizard, you can select columns to store in session variables. On each login page, make sure you are selecting the same columns.
by Default, the session names will be set to the same as the column name, if you do not change this, you will not have to worry about the names, if you do change this though, you need to change ot the same way on each login page.
As for creating a page with both login and register functionality, this can also be done.
Registration will use an Insert record server behavior to create a new user record, amke sure that the registration form has a uniquely named submit button and set the insert record trigger to the registration submit button.
Also make sure the login form has a uniquely named submit button and set the Authenticate User server behavior to trigger on the Login Submit button