I suspect that the will is clear, assuming it was drawn up by a solicitor. It is the family members themselves who usually muddy the waters by refusing to accept the terms of the will, or think they can do it better, but without doing it legally or who generally do not understand probate law.
In many cases the reasons are long festering family problems.
DH was executor to an uncle, whose daughter from his first marriage did not get on with the second wife and rarely saw her father. DH's uncle left a very clear will stating what objects in the house he shared with his wife (she owned it) were to be inherited by the daughter.
We meticulously followed the list and gave her everything on the list, but she kept claiming that anything in the house that belonged to her father should come to her - and we did hand over extra items, but all she was entitled to was what was on the list. This did not stop her telling us, and everyone else who knew the family in DH's home town that we were liars and thieves and had cheated her out of her inheritance.