No, you can't dispute this. The law doesn't care about the nature or quality of her relationship with him: that is irrelevant to the rules for who inherits when there is no will. And your brother's statement that you would inherit is also irrelevant--it has no legally binding effect. Only the designation of you as his life insurance beneficiary or a will leaving everything to you would ensure that you were the only one who received the insurance money.When there is no beneficiary designated, the laws says the life insurance money must go to the estate--the insurance company has no power or legal authority to do anything other than that.And if it goes to his estate when he had no will, it will distributed according to the rules for "intestate succession" (who inherits when there is no will). In your state (FL), it appears unfortunately that when there is a surviving parent and sibling, but no spouse or descendents (e.g. children), the parent receives everything: so likely, your mother will get the entire amount, unfair or not. If your brother wanted you to inherit, he should have made you the beneficiary or else had a will.