In 1934, Dumbledore's first worst enemy (and childhood lover) Grindelwald, unleashed ancient magic. Nobody knew exactly what he had done, and the magic lay forgotten after his defeat in 1945. But, in 1977 around Christmas, two teenagers in Hufflepuff came across an ancient spell while doing some of their Defense homework. Stupidly, they decided to try it and unleashed Grindelwald's dormant spell. A spell so powerful that it pulled three generations together. The year now is 2021, and Hogwarts just started to get three generations of new students...
In the year 2021, Hogwarts is suddenly bombarded with numerous students. Current residents wake to find their dorms filled with triple the amount of students, some that are recognizable as parents and other family members. They are all unconscious, so nobody is able to ask questions until the first wakes up.
The first person to wake is a younger Dumbledore, one that was transported from the Marauder's time. After he realized what has happened, the truth comes out. Now, the future generation waits, constantly watching a greatly expanded infirmary, for the rest to wake up.
When they do wake up, different stories are told. Marauder Era speaks of an rumored war and the Trio Era speaks of proof that Voldemort is back. Harry, Ron, Hermione, and Dumbledore know of the Horecruxes. Draco knows of his task, and now wonders how he will complete it.
In 2013, a Muggle Studies professor came up with an idea that would immerse the wizarding world within the muggle one, in a way. He spelled special journals for each student to use where they could talk with each other, or just themselves, as much as they wanted. Not all students participate, but it is open to any student to try if they wish.