I'm trying to find this manga that has been haunting me for months. It's about a kid (I can't remember if he was reincarnated or not) was kicked out of his noble house by his father but later on he become a noble. His father come to visit him because his heir did something and he came to apologize. When he went home the main character sends something to spy on him, he finds out his stepmom was controlling his dad using a drug, but that's all I can remember.
I believe this is Kyoukai Meikyuu to Ikai no Majutsushi, also known as Boundary Labyrinth and the Foreign Magician.
The main character left his home due to the actions of his stepmother and stepbrothers. After defeating a couple demons, the king bestowed a rank upon him. Afterwards, his father came to visit in secret. The heir found out about it and intruded on the meeting, insulting the main character and his friends. Due to one of those friends also being nobility, the father disinherited the heir. After arriving home, the stepmother tried to convince the father to undo the disinheriting. When he refused, she tried to poison his drink. Later we find the poison would have let her control him for a while.