Left hand thread lug nuts on driver side

So I've got some weirdness (at least to me) going on. My driver side front drum comes off without the hub. The passenger side doesn't. I thought this was an assembly. It does look like the studs are supposed to be pressed through through the hub and the drum. Am I correct in assuming this or are they supposed to come apart as two pieces? It seems like the service manual references "hub and drum assembly", which tells me they should be one piece. The fact that it comes off in two pieces makes me think I should replacing the drum too.

I should also note that the studs that are broken off are on the rear axle. Looking through the service manual, it looks like the studs on the rear are pushed through the hub that is connected to the shaft. Do I really need to pull the differential apart to replace these studs?

On a side note, the passenger side front also has what looks like a spring around the outside of the drum, whereas the driver side doesn't. What is this for? I don't see any reason for it or reference to it in the service manual.