I think you made a small mistake in example 2:
example 2: User A bids 1BTC for the two silver coins, User B bids 1.5BTC for the bearer bar, User C bids 2.6BTC for everything, User D bids 0.2BTC for the 25, 5 and 1BTC pieces. Users A, B and D win with a combined final bid of 2.61BTC
Which should actually read:
example 2: User A bids 1BTC for the two silver coins, User B bids 1.5BTC for the bearer bar, User C bids 2.6BTC for everything, User D bids 0.2BTC for the 25, 5 and 1BTC pieces. Users A, B and D win with a combined final bid of 2.7BTC
I will bid 0.2BTC for both redeemed cas 10 coins.
It might help to separate the items into lots
Eg: Lot A: Cas 10 coins, Lot B: Bar, etc.