So the ice cream thing earlier, both mother and daughter seem to be obsessed with the dead husband/father and tell him "soon (TM)". There's also all the bits where they talk about how the daughter looks just like her father.
The mother is glad her child was born a girl. Supposedly, the mother's weak constitution means she's unlikely to have another baby, which leads to the daughter telling MC she still has herself (to have a baby through).
We know mother and daughter are working together. Daughter mentioned MC looked so happy "last night" during ice cream scene (referencing sex), and mother pretended not to know, just suspected, she may have been caught while talking with MC's sister.
Pretty sure their plan is to rebirth the dead husband/father through baby with MC and daughter, hoping baby son will inherit the dead father's appearance given how alike the daughter looks to her father.
Edit:typo