I've had these plants for weeks and they were doing just fine. The purple-ish one has always been in the garden and has just been dying since day one of planting it as for the orange one I've had in the house but has randomly started dying so I've put it in a bigger pot and placed it in the garden. I was wondering if someone could help me as I really don't want my plants to die.
Thanks
Brad

Where are you located?, could you describe your climate as people will need to know that, to be able to give some advice.
How ever, the purple Celosia spicata is an annual plant, meaning that it will die after flowering finish in one season. There is nothing you can do to revive it, but they produce lots of seeds. When the flower-spike dried, rub them and you will find seeds. They are very small, brownish-black, and if you want you can have lots of new plant.

I'm based in North Wales, the climate on the otherwise. I mean it's been quite humid. Weather has been hot even on cloudy days. But it's been warm rain also.

Your plants look somehow dried out. Change the place your plants are now, water them on a daily basis each morning, and also add organic fertilizers to the soil. It might help stop plants from dying.

The first one is a Croton which is a houseplant in the UK. You've subjected it to all kinds of stress so it's struggling to adapt to all those changes.

The Celosia will die off normally at this time of year as it's usually treated as a bedding plant.

Your soil looks very dry.