Mumbai Darshan Itenerary

Dear All

7-8 adults, from South India (2 senior citizens + their children with spousess and Planning a Mumbai visit in September - October. What would be the essential landmarks / places of visit?

I plan to cover in one day- Gateway of India Marine Drive Elephanta Caves (Is fashion street worth including in this, for some trend street shopping for the ladies? It used to be good, but I dunno how it is today.)

What can I plan for day 2?

I'm thinking of a visit to Alibaug/Murud Janjira on day 3, if the beaches are still as good as I remember them to be (10+ years ago). Any opinions on all of this?

I'd appreciate valuable inputs, thank you.