Is there space for them to BOTH be right? When one sibling remembers neglect, they remember the details and the house’s emotional temperature; that is their experience. That is what they remember. It is true for them.
When the other sibling remembers a supportive environment, being praised, and the emotional temperature being warm, that is their experience. That is what they remember. It is true for them.
When we try to convince the other sibling that they are wrong, we are gaslighting them. Remember, every child in the same family has a different childhood. What your sibling says is true for them, but it doesn’t have to be true for you. Only you know what is true for you. You deserve to be backed by you.