Kind of stretching it to call this a 4th Amendment issue.
He can invite them in, and in that case, “plain view” doctrine applies. Any subsequent search would be covered by Fourth Amendment. Unless, there are exigent circumstances demanding action right then (like a trail of blood leading to the door, into the room, is the person alive? Will the person die if the door isn’t opened then, is there time to get a warrant. . .etc).
Tough call and there are exceptions. Without all the details of the situation I would not take a side on this one.