In your original post I think you said the SLW were a week old and the GLW were three. Looking at the pics I'd say both sets of chicks are a week or less. The GLW dont have any shoulder feathers showing yet, and they would at three weeks.
I have a couple thoughts. One, the chicks were already together so if there was some sort of bug they've all been exposed already.
Two, in my experience the first couple days is when you lose chicks if you're going to lose them.
I would suspect that the loss of the chicks was due to over heating, mixed with the shock of being moved.
I don't think there is too big of a size difference to mix your chicks, especially in this case, both Wyandottes. If the smaller chicks were say, bantys, then I wouldn't mix them.
If it gives you peace of mind to keep them seperated then do so. If it were me and the SLW were acting fine, eating and drinking, running about and not acting lethargic, I would not hesitate to put them all together in the apple crate.
It will be easier for you to keep one crate clean than two, and it will be easier to have one brood raised together now, rather than try to mix them later after they've been raised as two seperate flocks.
Keep me posted. Thanks.
Mike