I have two hibiscus trees that have been outside during summer for the last 2 years, and back inside the office for the winter.
When back inside they have white fly and bugs, the soil is drying out necessitating watering every 2 days, and leaves are yellowing.
Your two potted tropical hibiscus trees are experiencing a common response to their move from summer outdoor light, temperatures, and humidity, to the drier and lower light environment indoors as well as the tag-along insect problem.
Excellent information can be found on our Ask a Master Gardener website: https://www.torontomastergardeners.ca/askagardener/hibiscus-overwintering-on-balcony/
The two links provided in our website response provide detailed recommendations to cut back the branches and to thoroughly wash down the plant, possibly with insecticidal soap, before bringing it inside, may yet be possible given our current very mild December weather.
Good luck with your two trees.