Oh Shy, I totally understand family dysfunction. My family sounds a lot like yours and they could go on the Dr. Phil show or Montel...whatever. I have several that don't speak to one another, there are several I don't talk to and it is a vicious cycle. Your right life is way to short for the pettiness and fighting. Unfortunately, some people hold on to past hurts and harbor resentment for years and years. By the time they are able to over come it, if they ever do, it usually is too late as the relationship has completely broken down.
However, even though they are family if they are toxic to you and your kids than by all means cut them out. You do have a right to stick up for you beliefs and to be treated with respect and dignity. If they are not able to do this then what is the point of continuing a relationship with them? It really sounds as if you are being the better person and doing what you can by sending cards and reaching out. They cant even acknowledge this by returning the favor. Try to not let it get to you, I know it is hard especially when there are family functions times coming up. Your a wonderful person and a good mother and your doing what you can. If they cant understand that then it is their problem.
Hugs ~ Elisha
God grant me the serenity to accept the things I cannot change; courage to change the things I can;and wisdom to know the difference.
My thoughts and prayers are with you ,I hope you remain strong and focus on you and your sonand daughter and just your immediate family ,I know how difficult it is to have secrets hidden from you .It eats at you and you want to know what ?why? ...but dont let them all get you down .You dont need it