Everyone seems to be assuming there's going to be a lot of cash.
Inheriting property here, in the UK, can be expensive.
Probate, title transfers, taxes and other expenses means property often has to be sold to pay the duties and only then can any beneficiary inherit the remaining cash.
Property abroad can be a legal and financial nightmare, with confused titles, taxes, mortgages and legal fees all regulated and charged differently.
You don't say which country your Grandfather held property in, but your comment about different cultures rings bells.
Are the properties held in a country where property is kept 'in the family', rather than sold?
Will you be expected to sign property over to a male relative, regardless of how distantly related?
Are there any other relatives who could complicate matters?
This sounds like a fiendish nightmare without adding grief for your GF and your 'D'F's expectations.
I agree with a previous poster.
Your 'D'F needs to be told sooner, rather than later, that he is not entitled to any cash, if there is any and running his business into the ground in the expectation that you'll pay his debts will result in bankruptcy.
The attorney fees are going to have to be paid, property sold and that could take years.