u/Previous_Shirt_9507

If a book is published by two authors and both authors claim to have contributed to the work equally and in such way that it's impossible to separate the text into two parts, copyright term (at least in the US, UK, EU) will end seventy years after the death of the last remaining author, correct?

Would then adding a child to the book as an equal joint author (even as a fake claim) be a way of securing longer rights of commercialization for the family? Does this scenario have precedents and has it been tested in the courts?