Under certain conditions you may be able to claim non-children or other dependents on your taxes. Though it might depend on how much income they make, how much you have helped them out, and how much of the year they have been living there.
My parents claimed me once on their taxes as a dependent (not as a child) cause I was living there more than half the year, and because I didn't make enough money.
You might consider getting help filing your taxes, and filing them early, also if any of them are old enough to be filing their taxes, let them know you have claimed them as a dependent and already filed. If they file as not your dependent, the IRS may reject their filing, or investigate both of the taxes to sort out the situation.