Far fetched, but will keep watching.
Why did the husband leave after the (very small) funeral and go home to chat to the builder instead of going to the presumably (very small) wake?
Why did the girlfriend/mistress rock up as she did, pretending to be from the wife’s agency, wear the dead woman’s clothes, wander to the village in her pyjamas, swipe keys and go into locked rooms, use the computer (no password needed), sleep with the husband in the marital bed on the same night as the funeral?
Agree about the mother not seeming bothered about all this, she and the husband seem to be in some conspiracy.
I think it will have a daft ending, but will keep watching the next two nights. Might not have bothered if it went on for weeks.