First time claiming Luis and issac their father claims them every year but they live with me Monday through Friday I pay all their expenses food school etc

[abricasmk]

We told their father that he could not claim them any more but what if he already did what can I do?

[KristiK1 · Accepted solution]

If he already did, you won't be able to efile your return. You'll need to print out your return and file by mail. The IRS will then help you two sort out who is allowed to claim the dependent(s). 

Here is some more information on that process, including timing and eligibility rules: https://ttlc.intuit.com/questions/1899162-what-if-somebody-already-claimed-my-dependent