I'm thinking Radhaji is hiding in Mathura with her granddaughter Madhu. Meaning Radhaji thought the way things were with Rishbala they had too many enemies because they were public figures, so much had happened because of the fame, which culminated in RK and Madhu getting killed by someone that Radhaji didn't know whom, or she does know but doesn't want to risk harm to her granddaughter if that enemy is still there wishing her harm. So she decided to take her granddaughter away from it all.
But definitely Bittuji, his wife and child are enjoying there in Mumbai RK's wealth. Because Radhaji couldn't risk even to go to their house in Delhi (if your remember she mentioned this house before some months back), for fear their enemies would find them and harm them.