You start with the first situation, If the SSA-1099 is the only income. Then it is not taxable and you don't need to file. Then you can stop. It does not fall under the other categories and there is no other income. It is not unearned income. Unearned income would be mainly interest, dividends and investments.
See the top of the table in pub 501 Filing Requirements for Dependents - It says unearned income includes......taxable Social Security benefits....... BUT since you only get Social Security it is not taxable to begin with.
Social Security is only taxable when you have other income THEN.......
Up to 85% of Social Security becomes taxable when all your other income plus 1/2 your social security, reaches:
Married Filing Jointly: $32,000
Single or head of household: $25,000
Married Filing Separately: 0
