Tyson’s thoughts on his father are complicated. He hates his old man, but he bristles at any unprompted criticism of him; especially the Lucifer nickname. He respects his abilities as a professor, whilst also resenting how harsh a marker he was; almost failing Tyson for spelling errors, that could be counted on two hands over the course of a six thousand word essay.
He still gets nightmares about the beatings his father gave him, the most notable two being when Tyson came out as gay and when his father found out that Tyson was leaving to join the army: abandoning the family legacy. Yet some of his fondest memories are moments where he earnt his father’s approval, sitting in his office and playing chess against him.
He fights any positive thoughts about his father, but Tyson will proselytise about all the good his father did for Cambridge University. The ways he continued and added to the family legacy, and how far he went to help his best students improve themselves even after they graduated. But only his very best students.
Tyson doesn’t want to live in his father’s shadow, but he can’t help feeling that he wouldn’t be where he is without his father’s influence. He wouldn’t have joined the army to spite him, to prove himself without him. He adored his father as a child, always so desperate for his approval. It’s hard not to think of him as larger than life.
However, Tyson could never deny that - despite everything - no one could instil a love for mathematics as Professor John Delaney could. That is the only reason he could forgive his father; for the abuse he inflicted on his mother, his brother, and upon Tyson himself. For everything.
His father was more than just his teaching or just his family, a person: not two entirely separate beings. As mentioned in this blackmail headcanon, it was much simpler to forget that, to look to the Professor with deeming qualities and hold all his contempt towards the elder Delaney. Tyson doesn’t know what to do with John.
Jethro’s thoughts on his father are largely the same, but clearer and with less emotional conflict involved. The late John Delaney was an incredible mathematician and a great teacher, but an awful man and a worse father.
Jethro shares his father’s quick temper, but he hasn’t held onto the anger at his father. He left that part of his life behind. Jethro doesn’t feel like he owes his father anything, his accomplishments are his own. It’s in the past. It’s done.
He’s dead.