I can see why you’d want to rearrange things. How much budget did you have in mind? Are you on a slab or stumps?
In the short term I’d definitely close in the stair treads.

please include plans for upstairs and dimensions of all the rooms...it may be easier and cheaper to change the stairs instead of changing plumbing

Yes we are on stumps. As the Duplex isn't very big, we are really limited as to where the stairs can be relocated to. Also because the kitchen & bathroom really both need a makeover and new fittings, I figured we will be replacing any way. As for plans and dimensions I will look at getting those posted on here tomorrow. Thank you. :)

As oklouise says , you'd need to post more info , some sort of info about the plumbing , load bearing walls and the like .

Just at a quick look though , have you considered actually using Bed 2 as the new bathroom ? That may give you more options -- for example using under the stairs as an open office/study or even part of the lounge -- maybe a TV or couch there , and have the dining area in the opposite corner ? It may even be possible to use the existing kitchen area , walled in , as a new Bed 3 -- I realise it will still be cramped but 3 bedrooms may be preferable to 2 ?

Likewise , you may even find the bathroom won't need all of Bed 2 ( or 3 ) and could effectively 'step' that wall back , and still have 3 bedrooms but even end up with a bigger kitchen or bigger lounge ?

Just a couple of random thoughts .

The dimesions of the bathroom as is currently is 2.5 x 2.5. That's not including area where the laundry section is. It adds another 92cm x 140cm. Thinking may make this separate toilet rather than having toilet in the bathroom or, have the laundry left where is just turned around into bathroom area and wall the side that it is now accessed. Hope this makes sense. Appreciate thoughts and feedback.

Bigreader suggestion to fill in the stairs would make a big difference

I would consider extending kitchen into bedroom. Much easier plumbing wise. Staircase should never have had open treads. Maybe Perspex but do we really want to see up skirts.

There's more value in 3 bedrooms than having a bigger kitchen,

Can you exit to the side via lounge?

The exit is at front of stairs. There is also an external door from Bathroom/laundry. Only problem with having bathroom/toilet where kitchen is now, there is no window. Which I don't like in wet areas.

do you use the side entry and/or want to keep the side entry into the bathroom?

Basic drawing to keep the budget checked, I would keep the kitchen insitu, removing the return bench top and adding a bank of pantry cupboards. Access into the bathroom for the bedrooms needs to be retained. Both the bathroom and kitchen are 2.5 wide, so kitchen would have 600 deep pantry, 600 deep benchtop which gives 1.3 between them, Fridge remains in place

Some photos

One more

Without further dimensions for the ground floor, the following suggestion for your consideration. Move the kitchen into Bedroom 2, which would give you a sit up island. The bathroom could remain the same to service bedroom 3 and the family kitchen.

Add a 3rd bedroom upstairs into which is currently marked living.