announcing pregnancy to parent with cancer

Kaitlyn
So i need some help. Let me start off by saying i dont want any shitty comments. (You will see why i said this in my post) any rude comments will be reported. This is probably going to be long as well. 
My dad has cancer. He has had it for about 3 years. It started in his throat and has metastasized to his lungs. He keeps going in and out of remission to have it pop up somewhwere else. My mom just called me to tell me it has spread to his liver, his bone marrow is shot, so he isnt producing white blood cells to fight it off.  My mom did not say if they gave him a time, but i know there isnt much time left for him. I came to grips with it a long time ago. I know how this is going to end and i am okay with it.
My dad and i do not have a daddy daughter relationship, even in the slightest bit. He was physically and verbally abusive to me as a kid, and as a result i have lost respect for him. He ruined my childhood. We arent close and we do not get along. I dealtwith the  abuse until was 18 when he backed off because i was an adult. My mom didnt see the abuse as anything more than spanking and punishment so she never did anything about it and we never talked about it. No one knew except my friends. 
 
My mom wants me, my fiance and my 2 year old son to move back home to help her take care of him as he recieves at home chemo treatments. As of right now, they do not know im pregnant. Im almost 10 weeks. I was going to announce this week, but after this i  just feel like this isnt the right time, knowing he might not even make it to my due date in october. 
As much as he was an abusive prick to me, he loves his grandchildren and i know it will upset him knowing he might not get to meet this one. 
So i need help with when and how to tell them. I was going to do something cute for my mom, but idk if thats best now, given as this isnt such a happy time for them. Do i wait to announce? Or should i just do it right away? 
The reason why i included all that info was to show that we arent close, and that a cutesy announcement and all the lovey dovey stuff isnt what i neeed to hear. I know it sounds terrible, but please remember that you dont know the WHOLE situation and i only included the important parts. Please do not tell me that he is my dad and i should forgive him since he is dying. I dont need to hear that either.
Thank you in advance for understanding and again, any rude comments will be reported.