It is essential to speak to the academic advisor of each program: they will check whether your proposal has met all requirements for the specific program, and they are able to advise you in case of questions. Please also discuss your proposal program with the mentor of each program. They can advise you on the (consistency of the) content of the program. For some master programs it is required to discuss the proposed internal double diploma program with other members of the faculty, the academic advisor can point you in the right direction.
Indicate in the internal double diploma program form whom you have spoken to. This is of importance to the Examination Committees.