He was more of a father to me than my biological father.
「亡くなった父は私の母が再婚した3人目の父です。」= My father who died was my mother's third husband. / The man who died was my mother's third husband.
「その父は本当の父以上の存在でした。」= He was more of a father to me than my biological father. / Even though he wasn't my biological father, I consider him to be my real father.
ボキャブラリー
father = 父親
died = 亡くなった
mother = 母親
third = 3人目
husband = 夫
biological father, real father = 本当の父
more ~ than = ~よりも
even though = ~だが
consider = ~だと思っている