] ] And, by making Gert "co-jointress" in ownership with himself, after their deaths, it is G&C's children that will inherit castle and lands, not Hamlet.

] Isn't Hamlet supposed to be around thirty years old? Even if he's twenty, the chances of Gertrude having more children is small, and Claudius actually announces in front of the whole court that he considers Hamlet to be next in line to the throne.

There is a theory that she was a child bride to Hamlet the Elder, thus only in her early- to mid- 40's at the time of the play. Certainly biologically, the chances go down, but it is not out of the realm of possibility for G&C to have children. Even as recent as the last century, it wasn't unusual for a woman to bear children well into her 40's if she was physically able.