ah, mama, my heart goes out to you. What a crazy mess of emotions you are feeling and let me first say, all totally valid!
I don't personally think what you are feeling can be easily defined as PPD. You lost a parent when you were pregnant. What a confusing and crazy mix of things. Your grieving process got interrupted by a new baby and to top it off, you have one of those DPs, and I understand this, who doesn't quite know how to deal with all of it.
If I were you, I would definitely find some counseling ASAP for no other reason if not to sort everything out and figure out what feeling goes where, kwim? You, your kids and your DH deserve you well and after what you've been through, you need to allow yourself the space to do that.
What you are going through is so normal, please understand. Be easy on yourself, get as much help as you can afford(housekeeper, takeout, massage, etc) or garner from family and friends and give yourself the permission and space to grieve as you need to, ok?