Is it possible to have joint shareholders in a SMSF Special Purpose Company?

Yes, you can have joint shareholders. There are no laws in relation to SMSF shareholding. So you can do whatever you want. Joint is good if just mum and dad fund, so if one passes away, the other won't get caught up in probate. However, if you are doing Leading Member, then there's only one share and no joint as this gets cancelled and new share is issued to the next leading member.