Can anyone shed any light on this error? Bitcore Multisig - bad-txns-in-belowout
That error happens when the transaction attempts to send more Satoshis than it spends. You might have your units mixed up (using Satoshis instead of BTC, or vice versa). 

The code that throws the error can be sheen here: https://github.com/bitcoin/bitcoin/blob/v0.10.2/src/main.cpp#L1462-L1465