Hi, it's good to hear from you.
I am sorry to hear about your father. I hope he is alright.
You are right, if he has not responded to your messages about your father, he is telling you he no longer wants to be involved. Although his comments to you about his parents were bothersome, you probably don't want to contact them about the incident(s). This is because either one, they have moved on already and may not recall what happened, or two, you contacting them will just remind them of what happened and they may feel angry all over again.
If you sent an apology, you have no way of knowing how they will view it. Whatever happened is past, and since they no longer have contact with you, they may see your contact as a way of trying to get to their son, which may make you look worse. Or they could accept it. If you feel it is worth the risk, send it. But at this point, unless you see them again in the future, it's probably better you allow this to pass.
Oh, I know you aren't trying to get to their son. I am sorry if I came across that way. I only meant that you should consider that they may feel that way, especially if Todd likes to fabricate stories and may have told them something bad about you.
I am sorry you feel so sad. I know break ups are very hard and take a toll. Mourning a relationship is one of the hardest things to go through. But be assured that you will get through this and feel better in the end. You may always feel sad when you think of the end of the relationship, but you will be able to think of the happy times too and smile.