Okay if you have watched the first two episodes you will recall that sister #2 was wearing glasses
Pics from Episode 1
https://www.indiaforums.com/forum/ghar-ki-lakshmi-betiyann/423379/1st-episode-pics-25th-sept-06
By Episode 3 it is sister #3 whos is wearing glasses.
Please check it out and tell me if I am right.