He deliberately left his family out of his will - nothing! The people who brought him into this world(his parents) and his brothers and sisters were also ignored and they are all on a basic living!
Well families are a complex thing and we don't know who held what views and who sided with who over what?
You don't have an automatic right to anything just because you are blood. It's up to the discretion of the individual.
There are those in my family I'd leave nothing, because they are absolute toasters.
I am not making any comment on SG's family as I don't know them. His reasons are his own.