Your grandma is still with it, isn't she ? What does she think of this ? Did she say the cousin could take this stuff ?
When my grandma moved into a home, she divided up the assets herself as to who got what. That way it was like her will (only living), and that way she knew what each person would like and what stuff ment to them, and what it ment for her, for them to have and enjoy. Then when it came to more of a cull of her things, then a list was written and everyone could say what they would like, and if there was a double up, then it would get decided on. Each of us grandkids said what we would like, and most of the time got it. Gran also see us enjoy having those things too. I was specially given an oil painting, because I was with her when she bought it. I didn't necessary WANT it, but she wanted me to have it. So it is now in my hallway hanging up, and now that she has since passed, it means so much that she wanted me to have it. Same with her dressing table.
It's not the worth, it is the sentimental memories attached to those items. I would try and get the reigns tightened on your counsin, and tell her to hold up on all this crap, until you decide how to divy it up.
Not nice situation to be in at all. Good luck with it.