It depends. For your children, as long as no one else is claiming them as a dependent and they are age 19 and under, you can claim them as dependents. Regarding your ex-wife, here are the requirements for claiming an adult dependent on your tax return:
https://ttlc.intuit.com/replies/3288503
Here also, is information on the head-of-household filing status:
https://ttlc.intuit.com/replies/3288637
