It depends.
In order to file as married filing jointly with your spouse, you will need either an Individual Taxpayer Identification Number or a Social Security number.
The same information would apply in order for you to claim your children as dependents.
See the following link for more detailed information.
Non-citizen spouse and dependent
If you need to apply for a Taxpayer Identification Number, please see the attached form and instructions to request a number.
W-7 application
W-7 instructions
Please note you can attach the application applying for an ITIN when you file your return. You will not be able to electronically file your return. It will need to be mailed in.
As far as filing Single in 2018, you may need to amend the 2018 tax return. If he was legally married on December 31, 2018, he would only be able to file as Married Filing Jointly or Married Filing Separately.
Amend return
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