well they are intrinsically linked with you, blood and bone, so it is very very hard to disassociate yourself from them entirely. I hope you are using the toxic family threads as well - they may be of some help?
There's that lovely saying "they fuck you up, your mum and dad" - part of a poem by Philip Larkin (but having just read it the rest of it isn't particularly helpful to you!)
It's easy to say "don't let them get to you" but of course it isn't easy to do. It will be a gradual process of building yourself up to be the only family that you and j need, and it will take a bit of time yet.
Your mum is screwed up - obviously - and still hasn't accepted your situation, whether through obstinate bloody-mindedness or denial, I couldn't tell you. So she doesn't think beyond the end of her nose how anything she says or does will affect you, or how your situation might affect your reactions to events. I doubt she is playing deliberate mind-games with you though.
Ignore your dad, he isn't relevant - send a card or some flowers to your grandad but keep the message minimal. And if you choose to send flowers, the card with them will be addressed to your Nan anyway, saying that you are sad she has gone, or you will miss her, or something like that. Flowers are always to the person whose funeral it is, in my experience.