Thank you for writing.

Here is a general reference.  https://extension.psu.edu/ficus-diseases

It appears that the plant is near an older window that is not triple paned. If the temp gets below 40, the plant can have cold injury that looks like this.  https://plantcaretoday.com/cold-hardy-tropical-plants-effects-cold-temperatures-plant-growth.html The stringy nature of your plants suggests it is not getting enough light.

Those black areas on the leaves are suggestive of pseudomonas (bacteria) leaf spot. This gives some management suggestions.  It may be that the soil is infected.  The plant should be taken out of the pot, washed, dead roots and branches trimmed with a pruner that has been cleaned with alcohol and repotted into a carefully scrubbed, well draining pot with sterile potting soil https://edis.ifas.ufl.edu/pdf/PP/PP30800.pdf  

Note: I cannot tell if or how the current pot is draining.  Another possibility would be root rot from a plant that over time has decomposing roots lying next to the active roots.  Write back.