"my Dad and I..." or "Dad and I..."?

"My dad," because, "Dad and I," implies that the person you are speaking with has the same father as you.

MY dad and I

If you left off the MY, then it would also be correct to say, "Sister and I are going...."

That doesn't sound right, does it?

The correct way to refer to your dad to others is MY dad and I...

because of the fact mothers are maternal! they had us, We got here from there womb, They went threw discomfort for us... maximum folk have sturdy relationships with there mom because of the fact there dad is many times at artwork mutually as shes at domicile looking after the youngsters. maximum infants now days incredibly do not know there dad, because of the fact such a lot of infants have become knocked up!

when talking to people not related you say my dad. when talking to siblings you just say dad

Yes you're correct. when talking to people not related to you, you're to use "my Dad" insinuating possession. But when with close relatives such as your siblings "possession" isn't necessary because your Daddy is Daddy to your siblings too. This way you're comfortable. you'll find that when speaking to relative who are not that close you'll use "my". So it all stems from "possessive" how you feel....

I would go for the more formal "My Dad and I".

"Dad and I" is more casual and not suitable when talking about your father to strangers.

Using the relative pronoun"my" is correct when talking to strangers.

my father and I, would actually be the correct way to say it, if it's not an interpersonal conversation.

if it's quite personal, and you know the people well, then you should say, my dad and I.

Dad is yours anyway isn't he? So I don't think it matters that much.

Dad and I - your dad is your dad regardless of who you are speaking with.