they like to flower on new growth - so the pruning should help. the fertilizer seems a bit high on the last number. I honestly don't feed mine a ton unless they are showing poor growth signs, chlorosis/ or deficiency. Some varieties are also just like that :)

Hibiscus don't like a lot of fertilizer, they burn easily. Their leaves will turn a yellow green if they get too much fertilizer. Trimming them should help them to branch out nicely. And merkity is right, some do just grow spindly like that. The single red and the double peach bush out nicely. So do the el captiolios

Well I did cut them back and I feed them once a month. They are slowly coming out. I got this fertilizer from the Houston Hibiscus Society not sure the name is correct. I feed them once a month.

I would half the fertilizer dose for a bit at least. see how the growth changes.