About his scenes with Rhea&Alya those are just to show that he will always have a weakness for them,even after knowing their wrong deeds.
Stopped caring about Alya as he was before but still is his blood,can't break the ties with her definitive. Just tolerate her cause for now doesn't know how evil the daughter became thanks to her influence. Maybe he will discover some of her plans once Pragya comes back.
And the daughter...well no matter how bad she is,parents always love&forgive the kids,that's his case too. Again,she's his blood,nothing can change that,he will be deceived to see her true colors and maybe start to treat her like he treated Alya but not much can be done. Being a Mehra is enough to keep her around&unpunished.
Not taking his scenes with the 2 too serious cause Abhi is like that,emotional dodo,easy to fool for drama sake. If he would be too smart then no problems in Abhigya life. Same goes for Pragya,if she would fight for her marriage and let everything else on second place,then no need for them to separate.