You're mourning the same person and completely alone at once. Your sister wants to talk about mum constantly; you can't say her name without your throat closing. Your dad has gone silent; you think he's "in denial." He thinks you're "wallowing." Same loss, different griefs - and each of you keeps reading the difference as a verdict on the other's love.
It isn't. Grief styles are as personal as handwriting. Some people process out loud, some in private, some by staying ferociously busy, some by falling apart on schedule every evening. The person who cleared the wardrobe in week one and the person who can't open that door in year three loved the same amount.
What helps, practically: stop expecting the people who share your loss to share your grief. Get some of your support from outside the family - a friend, a circle, this place - so the household isn't each other's only oxygen. And when the difference chafes, try the one sentence that de-escalates almost everything: "We're doing this differently, and that's allowed."
You will grieve them in your way. Let the others have theirs. The love was never a competition, and the grief isn't either.