Inspired by a certain story

A couple gets married and has a child. Sadly, when this child is still a baby, one parent dies. The other parent eventually remarries, but, years later, tragically dies as well. Should the stepparent automatically get custody of the child? (Assume there's no obvious signs of being an unfit parent.)

ALTERNATE SCENARIO: The stepparent is not physically abusive or neglectful. (Their stepchild has a room of their own, albeit a basic one, and sufficient food and clothing.) However, the stepparent clearly favors their own biological children over the stepchild. Should they still have custody? What if the stepchild was responsible for all the household chores while the biological children did nothing except sit on their (rather large) posteriors?

If the stepchild would like to attend an important social event, but the stepparent says they cannot go unless they finish all their chores, and then proceeds to assign more tasks than can possibly be completed, is this appropriate parenting?

Also, should it be a matter of concern if the stepchild's "friends" are primarily rodents living in the walls of the family house?