I don't know. If the Garodia family is idiotic enough to believe Bhav in spite of Laxmi, Karan, and Saraswati's accusations, and despite the test results, there is no hope for them. If they would actually believe Bhav over their own 2 daughters AND son-in-law, they are truly horrific people. They are dumb, but I don't think they're THAT dumb.
The first person that needs to know the truth is Durga so if Bhav finds her or somehow tries to get her to drink the juice again, she will know better. They should tell her immediately and show her the test results. The only real reason Bhav has been winning is because Durga has been defending him. Once she starts to doubt him, the rest of the family will follow suit. They have no reason to trust him if his own wife doesn't.
They need to find Ranbir and get him out. Whoever is holding him there is only doing so because Bhav is paying them off, so all Lax and Karan have to do is pay him more. Once Ranbir is out, they can go with the test results and compare Bhav/Ranbir's backs and that will be it. Easy, but I guess not dramatic enough.