Still - do twins have the same/similar brain structure?

I would think those are the newborns who start out as close as you can get.

Indeed - and yet I'd think it's not close at all. I bet there is going to be the same level of variation as compared to relative differences between unrelated humans.

I would say it depends on what you call close.

The differences between unrelated newborns would be both genetic & environmental, compared to the identical genetics and nearly identical environments of the twins.

From which point all would begin to diverge further.