how can i add three existing windows form to tab control in Main form

Question

Hi friends,
         I have One main form  and there are some sub forms. I have already created the sub forms independently. In the main form i have menu controls.

For instance Main  form--Managementform
menu control in mainform - Management(main menu)
                     -student(sub menu)
                      -teacher(sub menu)
when i open sub menu student That contain three tab  pages. 1.for student personal registration,2.for student contact registration 3.studemt academic registration.  what i did was  three forms have been  created independently and  data transformed from login page to main page and main form to sub forms. now i want to add this forms to tab pages without loss of the data transfer between pages. because data transfered through form constructor methods. is it possible to do this? if so please tell me how to that.