Drupal 7 : i want to add the registration fields (username/e-mail etc) to a profile 2 registration form i am relatively new to drupal. So, here is my question : 

I have more profile2 types, assigned as roles (doctors/patients/partners etc). Each role has it's own registration form, shown at registration page, alongside with the obligatory fields of the registration (username, password, e-mail, etc...). For each role there is a unique registration path. The problem is that i want the registration form to be a multistep sort of "registration wizard". I have accomplished that with the multistep and field group modules, but this applies ONLY to the profile2 registration form. In other words, as the steps for the profile2 registration form go forward, the obligatory fields for registration remain at their position, below the form. I would like to integrate them as a step (the first one) of my multistep wizard. Any solutions???
I have achieved the above with a similar setup to yourself.

You state you have used 'registration wizard', so I assume you have created custom forms for the profile2 fields. Furthermore, you are validating and submitting the values at the end.

The simplest method is to create a custom form at the beginning of your process for username, email, password, etc. Then using the user_save() function. Of course you will need to ensure current users don't exist already, which is easy enough using user_validate_mail().

Hope this help.
Amarjit