One thing must be said about Italian inheritance laws of succession, they are very protective of the heirs' rights: nobody can deprive a legitimate heir of at least a part of the inheritance, even if the deceased didn't mention it or didn't want to.
What happened to you could never happen here. First, when your mum passed away, half of her estate would have become yours. Your dad could only have sold his half. Again, when your dad passed away, (but had he married that New Squeeze?), half of his property, including half of his money in the bank, would be yours. She or her family could only touch half of it. This, of course, IF they were married and she was a legitimate heir. Otherwise everything would be yours.