Is it possible to create private multi-signature transactions? Since ZCash is based on the bitcoin core it is also enabled to create multi-signature transactions by default. 

ZCash now adds the possibility to create also private transactions. 

But how to create private multi-signature transactions? Is it even possible?
Currently Private multisignature transactions are not supported. However, multisignature transactions are possible without the privacy.
It is possible to do a private Zcash spend to yourself, then do a globally transparent transaction (which could be a multi-signature transaction), and then the new holder of the funds (possibly you or possibly someone else) does another private Zcash spend to themselves.