He was Ritsuka's grandfather. He was shown to love her very much, and vice versa, and his love for her remained in spite of her being the grimoire. He also appears to've been genuinely concerned for her safety in life.
He was Lindo's grandfather and teacher in exorcism. In spite of him being the son of the vampire king, the professor loved Lindo, and wanted to help him overcome the darkness within himself. However, his methods often proved questionable, as they often succeeded in scaring Lindo rather than actually helping him.
The professor was said to've loved Maria the best out of his daughters, as is evident by his fondness for Ritsuka. He was always warm and cheerful with Maria, and helped her to raise both Lindo and Ritsuka. She was said to be the light of his life.
Even though he loved both of his daughters, Marta grew resentful and jealous of her older sister, because their father loved her best. This eventually resulted in her betraying the family, and having a relationship with Lord Nesta. The professor did not know of his youngest daughter's betrayal, and traitorous relationship with Nesta, until Lindo was born. It is implied that he was heavily disappointed in Marta for this, but still allowed her to stay with them until her untimely death. He was saddened when she passed.
According to Jek, Maksis got close to him because he wanted his eldest daughter, Maria. Over time, the professor began to warm up to him, and eventually allowed him to marry Maria. He did not realize that he had been tricked until it was too late.