If my children are filing their own taxes but I support them more than half of living expenses, should I claim them as dependents? (both students, one in another state)

You can use the tool at the following link on the IRS web site to determine whether you can claim your children as dependents. You have to do it for each child separately.

Whom May I Claim as a Dependent?

If you can claim a child as a dependent, make sure that when the child files his or her own tax return, they check the box indicating that someone can claim them as a dependent.