Prerna and Arti

Hello guys! So i havnt watched this show fully but so far, from as much as i'vve watched id like to know one thing. What the matter with prerna and aarti? Im not sure what ive missed since i didnt watch the first 2 weeks of the show and i've been missing a few episodes here and there as well which is why im confused as to why today rheas mom said mr.raichand has 2 wives or supposedly one is his wife and the other wife-like. And i think it was prerena or arti, not sure exactly which one is which, who was refering the other person as didi. Well why are these 2 living like this in the same house and one being the rude one and the other soft hearted i assume. So if there's a mystery behind this that hasnt been revealed then i guess ill have to wait and watch but if there's something that i do not know plz fill me in. As well as swho is shivin the son of then, arti or prerna? Thank you.

Mr. Raichand has two wives but only one is legally known. His 1st wife is Prerna who is the one everyone recogonizes as Inder's wife. Not much people know about the existence of Aarti. For your reference Prerna is the one with big bindi and Aarti is the one without bindi. Prerna is the rude one and Aarti is meek. Aarti is Shivin's mom but everyone thinks prerna is shivin's mom. Also prerna rules over the house as she has legal rights over the house and aarti is just technically Inder's mistress. I think in the heirs the one who plays aarti didn't know about Inder being married before and only found it after shivin was botn.