The MC ends up with both the red haired duke and the PTSD mage and, when she decides to go back to her original world, they both follow her.
The queen ends up dying from illness, but much later than she does in the original story. In the end, she becomes friends with the MC and, before she dies, the MC tells her her real name - which is apparently “Eugene” in the novel. Also, she gets some of her freedom back.
The male concubine (henceforth called “Blondie”) is actually some sort of immortal sorcerer. He was in love with a guy, and became sort of suicidal after he died. But then he met the king, who was the reincarnation of the guy he liked. So Blondie cast a spell on himself that causes all the men in the original novel to fall in love with him, which is why “all the guys around him are gay”. But, because he caused irreversible damage to his body, Blondie decides he needs a new vessel - so he impregnates the queen with, essentially, a clone of himself. This is why the baby doesn’t resemble either the king or queen. Blondie fully intends to transfer his spirit into the prince’s body so that the love between him and the king can “last forever”. Feel free to gag. The king and the previous nanny were in on the plan. However it when awry when the nanny had her pre-MC maid, who was bad at sewing, sew the magic circle needed for the ritual. Because some of her blood got on the circle, it was her who wound up without a soul instead of the prince. This is why the king and Blondie showed up and why the MC suddenly found herself in this situation. Eventually Blondie and the king try again, but this attempt goes even worse for them. Brown haired knight gets injured protecting the prince and Blondie’s spell breaks, resulting in him being horribly grotesque and their plans being found out. The Emperor then has the king’s titles revoked and has the two arrested.
The prince then becomes king, under the guardianship of the brown haired knight (who survived), the PTSD mage (who, like Blondie, is immortal), and the teacher guy. There is a time skip and, twenty years later, it’s about time the prince-turned-king get married. A comment about his type of girl results in PTSD mage getting depressed - since the conversation had turned to the MC. So the prince-turned-king lets him follow MC to her world and, because time works differently, he reunites with her and red haired duke mere months after they showed up in MC’s world.