In a Dilemma

My grandson's 3rd birthday is coming up on September 18th and I am in a dilemma as to what I should do. My married son and myself do not get along esp. after he got married 5years ago.. His wife is now expecting their 2nd child in October. Both he and his wife have not been talking to me as they have accused me of telling my sister that my Dil is pregnant when my sister saw her at a function. I understand my son did not want me to let anyone know but I was caught off-guard and told me sister. However, that same day I told my son about it and did say that I was sorry. However, he got very angry and accused me of gossiping with my sister. I was so upset for a few days and stayed in my room. I usually play with my grandson in the evening but I was too depressed to come out of my room. They then decided to keep him away from me. I texted my son a few days later saying that I miss my grandson and if I could play with me. My son texted me back with a very angry response that his son was not a toy. He also said that I was not a good mother and how can i be a good grandmother. He also said he will not forgive me ever for ignoring his son. I decided to not response back. My dilemma is that my grandson's birthday is coming up and I am not sure what I should do. Either way i know he is going to be very rude but I am trying to think what is the best way to handle his birthday. My son and dil are generally very unforgiving people and I am always the one apologizing first and usually it is always my fault. We have not spoken since May and I have not seen my grandson although they live in my house. Any thoughts?