Vadim Dolohov took advantage of the place in British wizarding society that he was offered with his advantageous marriage. Claiming all four sons instead of just Antonin meant that he had more leverage with his influential in-laws. He was hard on his eldest, expecting more out of him than any of the others. No one was positive what happened to Hermione's father-in-law. Before his son was thrown into Azkaban the first time, he disappeared on a trip to his native country and had never been seen since.