Simar is definitely one of the main characters. But I'm not sure about all the others as I haven't followed it closely.
The main character is Simar. There are likely other important characters such as her husband in the serial, and also her in - laws. Her mother - in - law would be an important figure as it is a family - centric serial. There could also be siblings - in - law or other relatives who play significant roles in the story's development, for example, they might be involved in family disputes or support systems for Simar.
In 'Sasural Simar Ka', Simar is the central figure. Her husband is another main character as their relationship forms a major part of the story. Then there are the in - laws. The mother - in - law often has a crucial role as she is a key figure in the family hierarchy. There might be sisters - in - law or brothers - in - law who add to the family drama, like they could be jealous of Simar or support her in different situations. Also, there may be some neighbors or family friends who come into the picture from time to time and influence the story.