Dry walls nail pops and wall cracks in ceiling doors and windows

FWIW, all the cracks look old, There is nothing looking at the crack that it is new. New cracks have their own "look" about them. Perhaps they were just overlooked before. These are typical cracks from settling.

About the posts, this is typical of older construction. New construction would have used pressure treated wood to isolate the wood from the concrete. The first pic show newer wood being used as a post that should or could have been treated, but there is no discoloration suggesting any deterioration or even beginning to. The angled post appears to have been a temporary post used to jack up the beam to add the post I was referring to.

Nail pops are also a very undesired thing that happens as well. It is not structural, only cosmetic. Curious how it is showing now, unless they have been there since the remodel, if the walls were redone. Never the less, they have been there for a while too, not necessarily since 1948. The nature of the paint reveals that.

Nails popping up above the surface is a common event and usually isn't cause for alarm. The reason this occurs is from slight movement of the framing members (due to expansion and contraction) that over time works the nail loose. Conversely, if the pops and cracks have appeared in a relatively short period of time, it may be time to search more closely for a structural problem. Where I live earthquakes and tremors are common. This quickens the loosening of nails.

Your crawlspace and the framing lumber in it look to be in good shape. This is pretty rare for a house built in the 1940's. I would guess it had some work done not to long ago. If so there might be settling issues that are causing movement.

I can't offer an answer for the dripping noise from your duct/vents. If it is the sound of dripping water it would be wise to verify the problem and repair it soon.

Hammer the pops back in slightly below wall surface. Than screw a 1 5/8 inch drywall screw about 2 inches above the pop. Screws hold better. apply joint compound, let dry, sand, and paint.