Sorry man, you are still grieving, I said something a little to soon, best advice for Your father, sister, and yourself would be counseling. I am not trying to say that you have any further problems, but it would help you and your Father/Sister. Again I say I'm living with my Aunt and Uncle at the current time, but my parents died when I was young, counseling has helped me get over some struggle I have had.
Im not trying to be a dick really, just tried cheering you up, it was immature of myself for saying such a hurtful thing at a time like this.
I am so sorry to hear this, I know how you feel, my father passed away 4 years ago in july... I know this must be so painful for you right now... I wish there was something i could do..