Ok after the original murder (the guy in model village looking like gulliver) the stroppy teenager (from the hotel) was speared to death during the annual boat race. She was the one that was shagging the dead giy (whilst he was alive of course) in the model village.
the little graves in the sisters' house (the sisters that owned the model village) were graves for 'dead' models put there by the old guy who looked after the village.
Someone put flowers on the grave and the miserable sister stamped on them.
The miserable sister was then in the family chapel praying and got walloped (and killed) from behind.
The old guy was seen running from the chapel.
Barnaby turned up to question him, old guy stood there with the weapon in his hand and blood all over himself and confessed to the murder.
Barnarby didn''t believe him.
It turned out that Bernince (the dippy girlfriend of the Hotel owner) was actually the old guys daughter that he had with the nicer sister years ago. She had to be given up for adoption as it wasn't accepted in those days.
The 'model graves' were put there by her dad (old guy) for her sake. She was as besotted with the model village as her dad was.
She killed the guy and the girl because they were desecrating the model village by shagging in it and she killed the miserable sister because she thought that was her mum and she was going to sack her dad.
There ya go
Good old Barnaby!!