If family members of a recently deceased person, enter the property of the deceased and take items from the property, knowing the contents of the Will - having found a copy in the property - and knowing that they are not beneficiaries of the Will. Would this be classed as theft and a criminal matter or would it be a civil matter?
It's theft, and therefore a criminal matter. The principal exceptions would be where there was no intent to permanently deprive the beneficiaries of the estate or where the persons taking the property had a genuine belief that the owners of the property would not object to them taking the items.