Daisy chain, it will go like this.
"Ok kids you can have half an hour screen time. What do you want?"
Ds will answer either 3ds, mums laptop, mums phone, mum's wii or tv.
Dd will answer mums laptop, mums phone, mum's wii or tv.
And yes the wii is flipping mine, I got it for the wii fit. For MY Xmas from my inlaws, five years ago.
If dd owns a tablet, will she ever choose it?
If not then I do not want it bought. She will learn nothing from it. No life lesson, no teaching her that she cannot pick and choose. It is her half hour screen time. She can use whichever screen she wants.