Is my step mom trying take my dad away?

I'm a 12 year old girl. I live with my mom and step dad. My dad recenly got married about 3 years ago. Me and my step mom have not had a good relationship and to make matters worse she just got diagnosed with cancer a very rare case. She tries to tell me that I'm the cause of my dad passingout because I have not told the truth and I am a snitch. I can't take it and one time I feel really bad about it though.I have a step sister and she likes to play house so we were playing house and all the sudden it it turned to a bf gf thing nothing was sexual because it would just be well weird and so she started to kiss me and she was pretending to be a guy so I was shocked on were she learned this from. So she told me ok so bow Im the girl so I tried to keep things simple like playing with barbies but Nooooo It got changed into what she did to me and my brother came in while we were pretending it was night time so the lights were off and he told my dad and my step mom found out what happened and my little sister palractically lied making it out tO be sexual assult and i did not even know it was tell after and I feel realllllyyyy bad about it and the next time I went to my dads house she made us sleep in separate rooms ( we usually share a room) so of coarse that made me feel that much more bad and my dad talked to me about it and he said it was a mistake every teen does it and he said even he did it and my dad had work that weekend so my step m had to take us to the airport. On the way she told me that what I did was so bad that they almost would not allow me to come back and visit my father that made me mad so I bursted in tears and my dad does not know half of the stuff my step mom says to me because I am so terrified she's going to call me a snitch again I finally told my mother about it and she told my dad and I was scared he would tell my step mom and she would hate me even more. What makes me feel like they don't love me is they forgot my birthday :( they don't ever cal.