There's no mention of the mother of the MC and his siblings, AND there's a single grave for the father. If she was buried with him, you'd think the MC'd give her his greetings like he does for his father, but nope. If this is adapted from a LN, I'm not going to search for it just to check if the author actually know that children don't spontaneously appears out of nowhere. I'll just assume they've got mommy issues, that's funnier.