AITA for not telling my Dad that he is now a grandfather?

I am 34M, I have a younger sister who is 28F. We have always been close, and she has been diligent about talking to me about important stuff in her life. <br><br>My Dad is... not great. He is emotionally abusive and demanding. I have been cutting him off from my life. He doesn't know about a lot of the big recent events in my life, including my recent marriage, my house purchase, or my upcoming divorce. <br><br>My sister is also cutting him off from her life, but this is a much more recent development. She is now actively avoiding him, and he doesn't know about any of the big recent events in her life, including her marriage. <br><br>She is also now a mother. She gave birth a few days ago, and she and her husband are service members. They are currently overseas and are not able to communicate with my Dad directly. She has me break the news to him whenever she doesn't want to, and she only contacts him directly whenever there are no real alternatives. <br><br>My sister has made it clear that she does not want my Dad to know about her kid until he is old enough to understand what my Dad is really like, and to ask that my Dad not be allowed around the kid until he can demonstrate that he is not abusive. She is also not going to force the kid to have a relationship with my Dad if the kid does not want one. <br><br>My Dad has asked me about my sister and her marriage a few times. I have told him that she is fine and that the marriage is going well. I have also told him that she is busy with her career and that she does not have time to talk to him. <br><br>Last night, he asked if she is pregnant yet. I told him that I did not know, and that I haven't asked. I said that it is none of my business, and that it is also none of his business. He had a melt down about that and is now demanding that I tell him. He has said that he will call the police on me if I do not tell him, because my sister must have gone missing if she is not communicating with him directly. I have explained to him that service members do not get cell phones and often cannot communicate with civilians directly. I have also offered to let him look up the base she is at so he can verify this, and he has said that he will call the police on me if I do not tell him. He has also asked if the pregnancy is the reason why I am not allowed to know about her marriage. I have told him that I know about the marriage, but that I am not going to tell him anything about it.