Q.Pruning Hibiscus
We are new to this home. The garden has two Hibiscus plants that are 9 feet tall. The bottom section (approx 12 stems each) appears to have been pruned at 2 feet. The remaining stems are at least double that number (24 to 30) and 7 feet tall have not been pruned at all. There are many stems going across the plants to the outside. They had only a few flowers this past spring and summer. However, they are now showing flowers at the ends of the stems. What and when should I do something?

I would wait until spring to prune and rejuvenate your plants.
Here is a link that will help you.
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/tips-for-pruning-hibiscus-plants-when-to-prune-hibiscus.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm