просто

var privateKeys = [
  new bitcore.PrivateKey('91avARGdfge8E4tZfYLoxeJ5sGBdNJQH4kvjJoQFacbgwmaKkrx'),
  new bitcore.PrivateKey('91avARGdfge8E4tZfYLoxeJ5sGBdNJQH4kvjJoQFacbgww7vXtT')
];
var publicKeys = privateKeys.map(bitcore.PublicKey);
var address = new bitcore.Address(publicKeys, 2); // 2 of 2

var utxo = {
  "txId" : "153068cdd81b73ec9d8dcce27f2c77ddda12dee3db424bff5cafdbe9f01c1756",
  "outputIndex" : 0,
  "address" : address.toString(),
  "script" : new bitcore.Script(address).toHex(),
  "satoshis" : 20000
};

var transaction = new bitcore.Transaction()
    .from(utxo, publicKeys, 2)
    .to('mtoKs9V381UAhUia3d7Vb9GNak8Qvmcsme', 20000)
    .sign(privateKeys);