Is it possible to have two "login" pages under the same hotspot? The first one without a login form and the second one with a login form.

What we want to accomplish is this:

1.) user is redirected to a first splash page with an option to buy an access code. No login form on this page. Let's call it login.html

2.) User clicks on a option to buy an access code and is redirected to external server where user will have an option to buy the code.

3.) After user makes the payment, user is redirected back to the routerboard but this time to a page with the login form, let's call it login2.html

Is this possible? Whenever I try to redirect to login2.html (before logging in), it redirects me to login.html.

Why not use the same login.html page and put a link on it to your server to buy time. Allow the clients through the hotspot using the walled garden to purchase. I did that for years. Worked for me.

That's what we are doing right now and it works but we would still like to separate the login form from this first splash page, if possible.

I don't see why you couldn't. You could use an external server to pass around the login variables. Here is a "simple" example that shows how to "pass around" the variables you will need to login.
http://wiki.mikrotik.com/wiki/HotSpot_e ... login_page

I don't see the reason for the first splash page with no login form. What if the user has already purchased time? What do you expect the user to do at that point? Buy again?