I'm am unsure how to explain to my semi-estranged dad how I feel about my half sisters?

say it to his face, why should you care about his feelings if he didn't care about yours. he left you and he deserves to be punched in the face, i'm growing up fatherless too. i also have other family members that my father had. i think you should at least try to talk to your other sisters, it is always good to have family members, even if you only share DNA.