I am mad on your behalf at your parents lack of sensitivity!
But if it is only going to cause a rift and more aggravation for you, maybe you could ask your Mom for specific items that you had in mind and just tell her they'd mean the world to you.
My cousin kept her Dad's antique car for 5 years, it did not run and she lived in an apartment and had to pay a garage to store it for her. She finally took a picture of the car and frame it and she let the car go, but she had to be ready, it was her way of grieving her Dad, and although it did not make sense to most people, even me, I respected her need to go through that, and helped her along in finally saying good bye (to the car) when it was time, when she was ready.
<<<HUGS>>> hoping you parents miraculously get sensitivity chips!
PS sorry just read all the posts, the box idea sounds like a good idea to me, it's there, you know it's there, and when you're ready you will open it again