What's your question? Ask

Yes, this is a very severe fungal infection. The course of action from here will be dolomitic lime and wettable sulfur applied together near the base of the trees, but not touching the trunk.

This treatment will recondition the soil along with destroying the infection. Should this be too vigorous of an infection, then the next method of treatment will require copper fungicides. These may also damage the trees.

Treatment will not result in the damage done already disappearing, but will stop new damage from forming. This may not be apparent for at least two weeks. You will know when all new growth looks unaffected.

This looks like a fungal infection, which can happen if the tree remains moist for too long. They tend to be mildly drought tolerant, and will not like to stay wet for very long. You can add wettable sulfur and dolomitic lime to the soil, to help cure the pest, and restore the soil to a more suitable condition.

This article will refresh you on their care: https://www.gardeningknowhow.com/houseplants/ficus/ficus-tree-care.htm

There are many reasons for dropping leaves and you likely have a combination going on.
Dry indoor air can be a big issue. Running a small humidifier for your indoor plants can help.
This article will help you.
https://www.gardeningknowhow.com/houseplants/ficus/ficus-losing-leaves.htm

This is unfortunate. I really need to see a picture to get a good idea of what is happening. If the tree is older, then it might need a transplant, or is rootbound and needs root trimming.

Sometimes they will even do this if they are moved from one area of the house to another. Sometimes, it just needs feeding, so if it doesn't get fertilized then this could be the issue, as well.

This article will, at least, help you to get started on a diagnosis: https://www.gardeningknowhow.com/houseplants/ficus/ficus-losing-leaves.htm

Yes, this will happen from a lack of light. They don't "winter" like other plants do.

What I would do from here is cut it down to about a foot tall. Then, take the tip of what you cut, and stick it in a pot. Keep the soil moist, but not wet, or completely dry. It will root itself very easily.

The bottom portion will also come back. Cutting back this far will force branching, which will make it bushier.

You will end up with two plants, and more if you aren't careful! This article will help you to care for the plant: https://www.gardeningknowhow.com/houseplants/rubber-tree/how-to-care-for-a-rubber-tree-plant.htm

Unfortunately for your case, this is a sign that the tree is very healthy, and aside from methods are can be very toxic to the area around the tree, there is no good method for controlling this.