You didn't see the ending. You just saw two brothers go to Rancher's house to find Rancher with Pia and MM who escaped from marriage, and found that Rancher is no longer the Rancher who studied and lived with them, and the people in graduation photo have been replaced by this strange Rancher. So they used this strange casket of the rancher's father to force him to tell the reason:

Rancher is not their brother's real name, and he is not a rich boy. He is just the child of a real rancher gardener.

Because he is eager to learn since he was a child, he has a talent for science and engineering, and he doesn't care about academic qualifications. He just wants to learn knowledge.

So the real rancher's father, the head of the family, decided all the tuition fees and subsidies, and let him use the rancher's name instead of the rancher to participate in various studies until he graduated from college and got a certificate. Then all the student status, degree and award certificates belong to the real rancher, and the gardener's son automatically left the rancher's home and disappeared.

Graduation photo also turned the gardener's son into a real rancher.

At the end of the story, everyone found the fake rancher who was a teacher in the slum through the contact information given by the real rancher. After being teased by MM, it was discovered that he was the inventor that MM was looking for hard. ...