| | Re: Past tense VS present perfect?
The first one isn't correct as, if you use "be up to" it should be "what", not "where".
"be up to " = do
What are you up to these days? = What are you doing these days? However, "be up to" often has the feeling that the person speaking disapproves - unlikely here as he's her boyfriend and therefore involved in whatever it is they ar doing. So let's stick with the verb "do".
If you want to use "where" the verb (here) must be "go".
So we could have :
Did you tell/Have you told your Dad what we are doing on Sunday?
Did you tell/Have you told your Dad where we're going on Sunday?
The choice of the first verb form depends whether the speaker is interested in the "telling" as a past event ....
You promised to tell your Dad about us when he came home yesterday. Did you tell him?
or whether he sees the present result of the past action as being the most important thing - ie he's interested in whether her Dad is now angry, pleased or whatever....
Have you told your Dad about us ? Is he OK about it?
So your explanation is right - but notice that it doesn't match your second set of examples. The first Did you realize he's a bad guy? is fine, but the second doesn't make sense. There's no easily imaginable present result of the past event of "realising". The person would either say : Did you realise.... ? or simply ask about the current situation : Do you realise he's a bad guy?