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It could be lack of lime, but it could also be either left over damage from winter cold or a lack of sunight. The sunlight is especially true if the tree or shrub is affected on the bottom of the plant. Sunlight does not get down to the lower branches through the upper branches and the lower limbs start to die.

Do you prune your conifers? If you do, you may have pruned the top too wide. If you do not, they may need to be pruned a bit to allow more sun to the lower branches.

Perlite can help with drainage. If the soil is staying too wet, this could be causing the needle drop. Make sure that there is plenty of drainage holes at the bottom of the pot as well.

Yes, wet summers can affect them by causing fungus or root rot. It may be a fungus on the needles or it can be a root rot of the roots.

Try treating the needles with a fungicide and check the roots for softness and rotting.

As long as the trees that had been there were not removed due to disease issues or there are no chemicals in the soil, it should be fine to replant now. This article has more info: https://www.gardeningknowhow.com/plant-problems/environmental/planting-in-old-spaces.htm

Unlike many deciduous trees and shrubs, most conifers will not resprout if cut all the way back to the base. Typically, pruning of conifers is only done as a last resort because of this and then it's only trimming for shape or to remove dead/diseased growth.

You can probably root prune some (so it fits comfortably), but I wouldn't take too much off. Also, the pot needs to be at least 2 inches larger than the rootball, though I would go slightly larger than this if you do not want to repot anytime soon. These articles have additional information that should help you: https://www.gardeningknowhow.com/ornamental/trees/tgen/growing-trees-in-containers.htm, https://www.gardeningknowhow.com/special/containers/how-to-grow-container-trees.htm