It's been known MC's mom was coming from a rich family. Him getting a possible inheritance that may have been hinted on Ep 1 is lazy writing? But her going 007 James Bond with crazy twists, faking death etc. is good writing?
It was never stated that her mother's side contacted him or his father. It was clearly stated MC's mom left his family to be with MC's dad, and she died giving birth. They probably hate MC and his Dad, cuz she's dead because of them. If it wasn't like that, they wouldn't let the memory of their daughter suffer from poverty growing up. Now they have no reason to contact them after 18-19 years, except she had a will that they couldn't find any way around it, and were obliged to abide the will.