I was given temporary guardianship of my brother's children, but the guardianship is only notarized not through the court. An argument happened with their mother because she didn't like that we sent youngest child to bed, so she said she will be coming to take her children but she doesn't have a home. Shes living on the streets bouncing between couches with her friends. With the whole coronavirus lockdown, I was wondering what my legal rights would be in regards to letting her take the children or being able to tell her no she can't take them.
Since you have only a temporary guardianship, it can be revoked at any time. It does not give you rights superior to those of the parent. Under the circumstances, if you believe the threat to render the children homeless is valid, you can apply for an emergency guardianship through the court system (which may be difficult under current circumstances). If she actually takes the children, you can also notify CPS.