copying data from old iphone 7 to old iphone 7

Hi there!

So i have my old device with my own apple id and i want to transfer all the data to my wife's old iphone 7.

I've made icloud and computer backup for my device and icloud backup for the 2nd one.

Here's my problem: the Apple ID used in the 2nd device which i want to transfer all the data too, is used also on my wife's new iphone 11.

Since the 2nd device doesn't have enough space to copy all, i need to clear and reset it.

I don't want this to do something to my wife's new iphone so i tried to disable icloud photos but since again, there's not enough space to download, my only other option is to delete from iphone. How can i know it will not make the photos disappear from my wife's new phone?

Should i make a backup from her new iphone then feel sure to delete it in 2nd device (her old phone)?