Hibiscus usually loses some leaves c any major environmental change. Do the growth buds appear to be in good health?
If so, then your plant is just reacting to change. In a week or so, it may just start replacing those lost leaves.
Check your watering. You may be over or under watering.
Is the soil soggy? Is it dry?
Does the pot have adequate drainage? Water should drain out freely when you water.
You might even want to check the roots for signs of rot.
And finally, get that poor plant as close to a window as possible as soon as you can until you can put it out for the summer. Hibiscus needs a full day's worth of sun and warmth.

Sorry I guess I forgot to mention they are in front of a window thanks for the advice!

Thank you for your advice you where right! They started re leafing today!