what was that in his closet?

a hippo probably

I think his brother's tongue, but I could be wrong.

Ashes.

it was a jar full of a liquid and something floating in it. ashes are usually kept in urns. so that jar is one full of formaldehyde to preserve a human body part I would say. from what I am reading and the shapes of it I got to see and from the details of the story so far I would say it really is his brothers tongue.