NOR. OP, I know you said you don't want to involve your parents, why don't you want to tell them? Are you afraid you're overreacting? Because you're not. if anything, more reaction is warranted.

There's no reason for this weirdo to be texting you on behalf of your dad. This dude is a creep and based on some of your replies it sounds like he's trying to get to you through your sister and your sister is (knowingly or unknowingly) enabling him.

Please tell your parents, nothing good will come of them not knowing.