The only critique to this offer I have is that the retail value of the jewelry is no longer applicable.  Assuming it's authentic, the re-sale value is unlikely to be evaluated as much (if any) more than the value of the precious metal from which it's made.  Being that this designer jewelry, it's safe to assume that new, retail pricing is far and above the value of the precious metals used to make it.  That may make your offer less appealing to a potential lender.  I would recommend to any potential lender (or escrow agent) to have the jewelry evaluated and appraised, which could add costs and time.

Also, it may behoove you to rephrase your offer to accept lenders from around the world, but you will need to find a trusted escrow agent in Germany.  I don't know if it'll make much difference, but it might.  I wish you luck with the help you need, but I doubt your offer is going to get much traction.

Maybe your brother can help you with the loan, since he's already in possession of the jewelry and aware of it's authenticity (not that he would need collateral since he's your brother.)  Have you asked him?