I think you need to give yourself a bit of grace here OP.
I've never had PND and I don't have kids, but I certainly know depression, so I actually cannot even imagine what you were dealing with.
I understand your family being upset with you, and for them yeah maybe it's a good reason to go NC, but for you it leaves you feeling hideously misunderstood and unsupported.
My advice would be to write a letter to your family and post it - don't email them, write to them all. The reason I say that is because if you email them, it'll be all too easy for you to get a tirade back from them whereas if you post a letter to them it'll give them pause for thought.
You need to be very balanced in your letter and tell them what has been happening to you, do not over egg it too much, choose to keep it to a paragraph max and choose your words carefully - explain to them how difficult this has been for you, some of the symptoms you've been dealing with, how the children are behaving and how it is has been making you feel.
Then spend more time talking to how they must be feeling, tell them you are sorry that your absence was so hurtful to them, that they must have felt abandoned by you and that you are so sorry for that. Don't say "I wish i could have been there or I am grieving as much as you", tell them that you all love them very much and speak to how they must be feeling about the situation.
At the end of the letter tell them how much you love them all.
Ultimately, my opinion is that their choice is born of grief and ignorance. If you write your letter from the heart, are honest and sincere, and they STILL choose to behave this way with you, then you have done all you can.
You know your reasons, you know how you were feeling and what you were dealing with, and at the end of the day if they cannot or will not empathise with that then they have not just lost one member of the family, but they have CHOSEN to lose another due to their own inability to see past their pride.
You can only do your best in situations like this, you can only try your hardest. Sometimes people aren't going to see your truth, sometimes they are unwilling to do so and that is devastating, but it is also not you choice when you have taken the time to explain things to them honestly and truthfully.
At least if you do this, you can know without a doubt, that you did your best and you tried to explain as well as fully acknowledging their grief, their sadness and their disappointment.
My feelings are that they just want a scapegoat for their grief right now, and can we all be honest: You don't need that, and you shouldn't have to tolerate it either.