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5 hours is generally enough to keep them healthy. They can take a little less sun, but you may see a decrease in flowering.

I'm sorry to hear about your plants damage and I'm afraid the news isn't good. You'll need to remove those branches.

Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm
https://www.gardeningknowhow.com/ornamental/foliage/yucca/propagation-of-yucca-plant.htm

It is probably getting too wet. Check the drainage to make sure it's not sitting in water as a result of all the rain. There's not much you can do about the rain, but once it stops, allow the plant to dry out some and remove all the dying foliage. Hopefully, once the soil has dried out, it will bounce back. However, these plants do not like to remain wet for too long and root rot can quickly set in.

Yes, you can remove the spent bloom. The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/foliage/yucca/yucca-plants-care-and-pruning-tips-for-pruning-a-yucca.htm

The following article should be of some help to you: https://www.gardeningknowhow.com/plant-problems/pests/mealybugs-white-residue-on-plants-leaves.htm