It is after much thought I am making the following post.
First of all, a 16 years old can think of an 8 years old, capable of betraying and telling lies. But after all these years, a grown up man putting the blame on 8 years old looks ridiculous, whatever big tragedy he had been through. OK, he is justified taking revenge from Indrani's family and for that he has used Chandani. He also has rationalized that Chandani has feet of clay , as she has abandoned her kid.
So fine. He is having his revenge. Yesterday's events never prove that it was Dev who took care of Chandani during the rituals. In fact it was vengeful and diabolical Advay, who knew about Sasha's arrival and was planning Chandani's heartbreak. The more he showed care, more will be the impact of the final blow. This was Advay's cruelty and devilish nature talking, not the caring side of Dev.
Coming to the marriage, a marriage performed by the priest is a legal marriage. There are witnesses too. Also there was a reception and Advay himself never denied the marriage. Such marriage is legal and people are advised to register the marriage for all official purposes etc.. but non-registration does not make it invalid. Advay himself declared in front of the crowd that he is leaving his wife after a night. So legally Chandani is his wife, till divorce happens.
To give Chandani self respect, the CVs should see that Chandani gives up her hopes on Advay soon. She should stop wearing his sindoor. Nani should insist that Sasha can not stay in their house and /chandani should continue to stay as it is her house. Chandani shoud enroll herself in a college/work some where and start rebuilding her life. Meanwhile Advay-Indrani confrontation should bring out the truth and he should repent like hell.