You do NOT file a joint tax return and then an amended joint tax return. You must file an amended return since you are changing your filing status from Single (which was incorrect if you were legally married, as it should have been Married Filing Separately) to Married Filing Jointly.
You Only file the amended tax return with a filing status of Married Filing Jointly. You include with the amended return the W-7 ITIN applications for your spouse and children.
If your spouse has income, either US or Foreign, that income has to be reported on the amended tax return when filing jointly.
The amount you paid for the federal taxes owed on the original tax return will be entered on the amended tax return, Form 1040-X, on Line 16.
If you have a tax refund on the amended return it would be entered on Line 21 and if you have taxes owed on the amended return it will be on Line 20.
