My dads dying..

Yesterday my sister over heard my dad was dying and had 6 months to live in an argument between him and his wife so they had to admit it to her but made her swear not to tell anyone she thought I had a right to know an told me, I'm so upset and don't know how to take the news.. Obviously I'm heartbroken he's dying but the betrail of them keeping it from me is killing me how dare they keep that from me! I've never got on with his wife since I was a teenager and I think she's thriving off the fact that she knows and I don't know! I'm 4 months pregnant an my baby has gastroschisis and will be born premature with intestines outside so I don't really need anymore stress and worry at the minute. What would you do confront them about it or ride it out..? I'm visiting them now and haven't said anything but just to see then lieing to my face is so frustrating and his wife keeps asking me have you spoken to your sister and who are you talking to on your phone because she's worried they'll tell me I don't know what to do help :( x