My guess is that they both want to become mothers at the same time and every time their „victim“ caught wind about it, he flees from them (that’s why they burn all his clothing bc he lived there with them and they want no evidence of it).
The mothers saying of acting fast is maybe bc of her age not having much time left to get pregnant.
Could also give the opportunity to have a former victim approach the mc at some point for a crazy arc, where mother and daughter going full nuts.
Well all just assumptions, the murder route is also possible but not as likely atm.
I hope at least.