Who qualifies for Social Security survivor benefits?
Whether or not a surviving spouse is eligible for Social Security survivor benefits depends on age and circumstances. In general, a widow or widower age 60 or older (age 50 or older if disabled) is eligible provided you were married at least nine months.May 28, 2014

https://www.schwab.com/resource-center/insights/content/who-qualifies-for-social-security-survivor-benefits

Common law spouses and former common law spouses can be eligible for Social Security benefits (dependents and survivors benefits) based on their husband's or wife's earnings record, if their states' common law marriage requirements are met.
https://www.nolo.com/legal-encyclopedia/common-law-marriage-social-security-dependents-survivor-benefits.html

How much will I receive?
We base the benefit amount on the earnings of the person
who died. The more the worker paid into Social Security,
the greater your benefits will be.
Social Security uses the deceased worker’s basic benefit
amount to calculate the percentage survivors can get.
The percentage depends on the survivor’s age and
relationship to the worker. If the worker who died was
getting reduced benefits, we’ll base your survivor’s benefit
on that amount. In most typical claims for benefits:
• A widow or widower, at full retirement age or older,
generally gets 100 percent of the worker’s basic
benefit amount;
• A widow or widower, age 60 or older, but under full
retirement age, gets about 71-99 percent of the
worker’s basic benefit amount; or
• A widow or widower, any age, with a child younger
than age 16, gets 75 percent of the worker’s
benefit amount;
• A child gets 75 percent of the worker’s benefit amount.
https://www.ssa.gov/pubs/EN-05-10084.pdf