code: public OmemoMessage.Sent encrypt(Set<BareJid> recipients, String message)
              throws CryptoFailedException, UndecidedOmemoIdentityException,
              InterruptedException, SmackException.NotConnectedException,
              SmackException.NoResponseException, SmackException.NotLoggedInException {
          synchronized (LOCK) {
              LoggedInOmemoManager guard = new LoggedInOmemoManager(this);
              Set<OmemoDevice> devices = getDevicesOf(getOwnJid());
              for (BareJid recipient : recipients) {
                  devices.addAll(getDevicesOf(recipient));
              }
              return service.createOmemoMessage(guard, devices, message);
          }
      }
docs: OMEMO encrypt a cleartext message for multiple recipients.
  
  @param recipients recipients barejids
  @param message text to encrypt
  @return encrypted message.
  @throws CryptoFailedException    When something crypto related fails
  @throws UndecidedOmemoIdentityException  When there are undecided devices.
  @throws InterruptedException
  @throws SmackException.NotConnectedException
  @throws SmackException.NoResponseException
  @throws SmackException.NotLoggedInException