Hi Danielle,
Well you have had a great response from the forum to your issues. The bottom line is that you have a duplex under a registered Strata Plan Title.
It seems to me you have a good working relationship with your co Owner, thats a great start. I think what is best for you both is to sit with a good Strata Lawyer and talk about the outcomes that both Owners want to set in concrete so when one sells the other is protected. That is a great Idea!!!
If you want a couple of Strata Lawyers firms names send me an email and I can give you a couple that know what they are doing and wont skin you and your co owner alive.
Best for the future and thanks to the forum members for their contributions as always.