What’s happening to my sunflowers?

I have 3 sunflowers which were growing beautifully from seed but 2 have started wilting and the third one is thriving? I’ve done nothing differently, they are in the same type of pots, watered regularly and were all together in the same spot.

Yesterday I noticed the wilting and curling of leaves so I moved them out to the shade and gave them some water. This morning they were back to normal until an hour ago I thought I’d move them to a sunny spot and now they’ve started wilting again.

Do I water them again? Scared I’ll overwater them. Not sure what is wrong with them? You can see the difference between them in the photos.

Thanks!