First of all, chachiji is kapil's step mom..so one cant expect her to behave with her children as a real mom does...but she's very evil. She is using kapil for gettig all that she wants..she doesnt care about anyone else. But I guess she wants to show herself as a very good mom in front of chachaji..so as soon as chacha entered she started behaving nicely with kapil.
And as for rev and anu they are the step-daughter and step-daughter in law respectively...so how can one expect her to be nice with either of them??