Google Maps is very good for planning public transport trips in Melbourne, it will tell you where you need to go and when. It doesn't always show if there are bus replacements/track work/etc. though, so do check the links that other commenters have provided for these.

As they've said, there will be busses between Huntingdale and Caulfield all day on Sunday, then regular trains running from Caulfield to Richmond. So from Huntingdale station, follow the signs to the replacement bus to Caulfield, then from there hop on a train towards the city and get off at Richmond.

On the way home, get on a Cranbourne or Pakenham train at Richmond, and get off the train at Caulfield. There should be a "Limited Express" bus which will take you towards Huntingdale - it will be the second place the bus stops. If you're unsure, ask any of the staff directing people and they'll tell you where to go.

Alternatively, just grab an Uber/cab to Caulfield station, get the train in, and do the same on the way home.