Deceased Parents And Sibling Guardianship Questions

Location: Minnesota

My fiance's step mom passed away three years ago from cancer, and his dad passed away November 5th due to complications from a car accident he was in back in June.

My fiance had moved back in with him in August to help him out due to his disability. His step brother lives with him too, but he is a long haul truck driver who can't be home all the time.

My fiance's 11 year old brother has been living with them since his dad's death and going to school like normal with no CPS or state action. A social worker came and talked to him 2 days after his death and seemed like she wanted to take the kid, but he had legitimate reasons not to go with her at the time. They expected her to come back another time, but it's been over a month, and they haven't heard anything new from CPS. The school knows his dad passed away and offered him counseling. They haven't contacted social services to put him in foster care or anything.

His "godmother" is his aunt, who is retired and physically disabled and lives in a tiny cottage across town from them. They visit her frequently, but she doesn't actually have anywhere for the kid to sleep. He only ever stays over in the summer when it's warm enough to sleep on her hammock or deck. Is she technically his guardian now or do they have to file something in court and make it official?

The adult brothers are inheriting the house and land and want to keep living there with their little brother for stability if it's legal, and their aunt agrees. I read online that there's a long process to get a home approved for sibling adoption, but does also apply if he's just living in the same place he always has? Do the brothers need to file something with CPS, a lawyer, or what?