You are correct that the raisins would have other constraints to keep it from infitatly expanding into nothing. Not because it's not expanding but because it has external constraints like gravity keeping it there.

They do have expansion applied to them, but gravity and other things effecting space time would be keeping it on place.

As for attoms, I think you picture something solid. But there's not. The electrons are getting further from the nucleas, but it's still bound quantum mechanically to the attoms regardless of its position.

But then the nucleas isn't soldi either. It's made of smaller things yet, and so on and so forth. So inside would also be expanding. But again other forces at play would bind things together.

The expansion is also not a force. It can't overcome other forces so it keeps things in line.