Actually it's more bc MC's mom is smart (iirc she comes from merchant family) and she's good manage the money, household, she's a real waifu material, so the grandpa forced MC's dad to marry the mom.The grandpa and grandma loves the mom so much, but too bad MC's dad is a scum, he brought back a concubine, i think she comes from brothel or sth?? The dad couldn't manage the house w/o MC's mom, and tossed all troublesome things to the mom while he himself only care about his face, connection and his concubine. Also, bc the concubine keep doing the pillow talk, so dad neglect MC's mom more.
The grandpa is a taifu (grand tutor), but bc his son (MC's dad) and bros didn't have any talent, so their home actually only have title w/o an actual power like when grandpa was a taifu. But after MC succeed being the youngest taifu, dad started want to get close to MC, ofc MC ignored him. MC even told his mom that she can divorce the dad if she wants to. MC+mom separate themselves from the dad after the grandmother passed away, btw the grandma also left letter or sth that she agreed if MC's mom+dad separate.