If it is in your fathers name then it is part of the estate and she cannot do what she wants.
It appears she is trying to claim the land under adverse possession.
The caretaker should report him to the police for the assault.
You should also report their actions to the council .
If the items have a value then you can ask her to pay it back to the estate.
You can also get an order to stop her and her husband going near the property.
The caretaker has to report the assault and also the theft of his own items.
I hope this makes sense and is of assistance. if there is nothing further
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