Kenamen20: and your sister the USC widow

good evening VO. my sister lost her husband(a us citizen) 4 months ago they were both residing here in lagos because he couldn't work over there anymore after he got disabled, they have four kids age 10,8 (twins) and 6months old baby, the first 3 got their us citizenship here through neutralisation but the baby doesn't. NOW MY QUESTION IS what visa category can the baby and the mother (she has never travel out of Nigeria before) apply for since the other three are citizens NOTE: she's not working, when her husband was alive they where living on SSA benefits(the husband and three kids) and will the US government stop paying since the husband is no more .. pls help a brother because she does know anything about the process at all

I posted a very extensive answer to it in a wrong tolic and it was deleted. I will repeat it here in case somebody needs this information.
US citizens widow / widower (yes, the man widower is entitled to all benefits too, not only not working wife widow, working female or male)

Sorry about your lost. AS a US citizen widow your sister and her kids are entitled to all kind of benefits including the green card self petition. Yes, your sister and her kids can apply for a green card and move to US but it needs to be done no later than during 2 years after her husband past away.
"If you were married to U.S. citizen before the citizen’s death, but had no I-130 petition filed on your behalf, you can self-petition as an “immediate relative” on Form I-360, Petition for Amerasian, Widow(er), or Special Immigrant.

To qualify, you must not have been divorced or legally separated from the U.S. citizen at the time of death. Your eligibility to immigrate as a widow(er) ends if yout have remarried. You must file within 2 years of the citizen’s death.

If your citizen spouse did not have a Form I-130 pending at the time of death, you must file the Form I-360 no more than 2 years after the death of your citizen spouse.

If, however, you were married less than 2 years, and your citizen spouse died before October 28, 2009, you must file your Form I-360 no later than October 28, 2011."
https://www.uscis.gov/green-card/green-card-through-family/green-card-through-special-categories-family/widower#without%20pending