It is also possible you may use the "Head of Household" or "Widow/Widower" filing status in later years rather than Single. There are certain requirements (like qualifying dependent) which must be met for you to qualify to use these statuses, however.
What you're doing here is really dangerous for you, because as the above demonstrated, tax rules can get complicated and many circumstances you didn't realize are relevant can change your tax benefits or liability significantly. Another example is the "kids who do not live with you", but if you're filing jointly with your spouse and they lived with them, then they do live with you! And of course there is the health insurance individual mandate. And then what about foreign income?
Also, have you or your spouse filed in previous years? The final deadline to file or amend for tax year 2015 is coming up April 15, 2019. Amending means things such as claiming a tax credit that was omitted on the original return or changing the filing status from filing separately to filing jointly, which can only be done until that final date.
I understand that you're still dealing with the death and all, and probably would rather just skip the taxes this year if at all possible (or rather, defer doing them until next year). However, this community is not the correct place to get advice on what you should do or are required to do, rather it is a place to ask general questions on the tax law and procedures and get opinions on what might be appropriate. I've said earlier, and I'll say again, you should get professional advice or at least go through the tax software interview process to get the best picture possible about what filing taxes would mean for you and if you owe anything. If you don't understand something in there, then ask a specific question about that topic, not a generalized question like "AGI is all that matters to determine if I need to file" which is very open-ended.