You have made few valid points, Abida.
Mama mami are not going to approve Naina so soon, they will create problems for sure. The way recently mama mami has started to change their colours shows that there is something coming up. Mama mami might take su name and Su Naina confusion is on the way.
But Sameer will not let the confusion prolong, it was clear that he just needs Vishaka's approval and if anyone else disapproves then he doesnt care and will handle it.
Nanu's approval of Naina is also very important, if Su confusion plays out then Sameer will not succumb to his family demands and might tell Vishaka everything about his relation with Naina and how Nanu accepted her. Already without any major hurdle itself Sameer wants to tell everthing to Vishaka and if the confusion comes up he will definitely not keep quiet.