excursion help

I did read the post about the islands but i was looking for a bit of extra help

Hey everyone so my mum Aunt and I will be heading to the south pacific for a cruise. On Royal Caribbean taking in Noumea, Vila and Mystery Islands. My Aunt has never cruised before and the only south pacific island I think she has seen is Fiji for her honeymoon 40 years ago. (she is now divorced) Now my mum have done the South Pacific before on P&O Noumea Lifou and Vila. We loved Vila. We went to the water fall and stood under it then did a little duty free shopping in ton before catching a taxi back and shopping at the wharf markets. We didn’t have a good impression of Noumea. We did a city tour but our ship docked late afternoon. It was lightly raining and got dark quickly so didn’t really see much. We want to change our opinion on Noumea

So I am looking for some budget friendly things to do. (budget as cheap as possible without being nasty or dangerous. My mum says aunty is on a budget but doesnt give me an idea on how much)

I think we may book 1 excursion through the cruiseline but just get off the ship and walk around for others. Now I have figured out that Mystery island will be a good one to just walk around the island. We all like walking and my mum is into plants and gardening. Can we literally walk around the entire island in a loop or is their obstructions. And is it safe to slimly walk off on our own. I was also going to go snorkelling with my own gear while mum and aunt just kick back on the beach. Ive only been snorkelling a few times however.

Noumea or Vila. Is there an island that its best to book a shore tour for as there isn’t much to do around the port or easy access to where there is stuff. We are 3 woman and want to be as safe as possible. I do like nature and exploring. My mum is into history and gardening. My aunty is into art. So I am trying to find something for all. Whether its through the cruiseline on our own or on the day.

Help?

Oh also money. I remember using my credit card at the duty free. Umm i think I used Australian money at the markets. It was 5 years ago so I was wondering if they still will accept that payment method at places