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You can try pruning to create more growth but you should also look to figure out why it lost leaves in the first place. With plants in containers, my first thought is that the plant is under or over watered. Under watering often occurs because sometimes people do not realize that container plants outdoors in summer need water frequently, often daily or even twice daily. Overwatering is caused when the container does not have a drainage hole or the drainage hole is blocked and the plant ends up in standing water in the container. Both of these things can cause defoliation.

If you can correct whatever is causing the leaf loss, it should regrow its leaves. Even with pruning, if the cause is not corrected, the new growth will be weak.

This article will help you with pruning:
https://www.gardeningknowhow.com/ornamental/shrubs/holly/trimming-holly-bushes-how-to-prune-holly-bushes.htm

If you have had a lot of rain, it can cause problems with leaves. Too much water causes iron chlorosis. This article will help you fix the problem:
https://www.gardeningknowhow.com/ornamental/shrubs/holly/holly-yellow-leaves.htm

There are a few things that can cause this. Holly scorch is the most common. This happens when the weather changes too quickly. Newly planted shrubs may be more susceptible. The plants should recover from this on their own. Give them a good dose of fertilizer to help them get back to full health.

It sounds like the plants have a fungus that is causing leaf drop. There are a few that can do this, but they all can be treated with a fungicide. Treat the plants with a fungicide.

There's not a lot you can do that doesn't pose a risk to whomever is trying to actually remove the nest. It's better to wait until they're least active, usually at night or during cooler temps. This article may offer some suggestions to help you; otherwise, you may want to seek a professional: https://www.gardeningknowhow.com/plant-problems/pests/insects/kill-wasps.htm

Vertically. This article will help with your cuttings: https://www.gardeningknowhow.com/ornamental/shrubs/holly/holly-cuttings.htm

Do not transplant them out until the cuttings have rooted. Hollies should be spaced 2-3 feet apart, depending on the variety used and overall size.