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Yes. Generally, the root system will extend at least as far as the canopy of the tree (if unpruned), but some may have a root system up to three times as wide as the canopy, or drip line of the tree. However, with crepe mytle trees, there's no need to worry much about invasive roots, as their root systems are not aggressive, meaning they are not strong enough to pose any major threat to nearby structures or plants. Nonetheless, while they do not usually have an extensive root system, it is always recommended that they be planted at least 5-10 feet from foundations, walkways, sewer lines, etc.

They typically can live about 20 years. Their life span can be lengthened and shortened by the care and problems they encounter, but this is the average.

You may be lacking phosphorus in the soil, which is necessary for blooming. Give the plants some phosphorus-rich fertilizer or add some bone meal to the soil around them and this should improve the flowering.

Hope this article will help: https://www.gardeningknowhow.com/houseplants/hpgen/preventing-mold-in-the-soil-of-a-houseplant.htm

I would recommend waiting until spring to cut them back. First, I think we can expect this winter to be a bit harsh and unexpected yet to come. Cutting now will remove any protection the plant has from the cold in terms of dormancy. Pruned plants come out of dormancy and, while oleanders don't have much cold protection during dormancy, if you get another cold snap, they will need even the little they have. Second, you will have trouble fully assessing the damage. Just because the leaves die back does not mean the stems have died. In the spring, you can better assess which stems are re-foliating (i.e. are not dead) and which are not, and then remove the ones that are not producing new leaves.