Any raw data stored in a MultiChain blockchain is visible to every node in the chain. By the way, it's exactly the same in Ethereum – even if you think you've hidden access to that data behind some smart contract, the data itself is still stored on every node's disk and can easily be read by nodes that wish to.
If you want to hide information on a blockchain, you should use encryption. If you want to manage selective disclosure over a blockchain, but only store each piece of data once, you can use a combination of symmetric and asymmetric encryption as described in detail here: http://www.multichain.com/developers/stream-confidentiality/
Assuming you're creating a permissioned blockchain, the consensus mechanism is round-robin mining between permissioned nodes, with a customizable level of leniency to deal with non-functioning nodes. See the mining-diversity blockchain parameter.