I wouldn't keep them outside if temps ever go down to or below 55 degrees which is indefinite in KY
. Ficus trees while being very forgiving in general are still only hardy as tropicals. The only real factors for caring for tropicals indoors would be to make sure they receive good light exposure and have a good soil mixture that dose not stay wet for too long, as the soil will take longer to dry if it is indoors during the winter. Light while lower in the winter should still be adequate as Ficus's are forgiving with light and most varieties in general prefer lower light levels.
Only fertilize the trees as much as once a month instead of the twice every month regiment and do so with a fert. that is low in nitrogen. Low but not absent in nitrogen since even though they will be growing very little they still will be growing and benefit form a slight dose of nitrogen. Something like 2-10-10 would be ideal.