We co-own a patent or application. What can each of us do?

Co-ownership works on a default set of rules that an agreement can change. Start with what you are trying to do.

Moderate complexity - several routes or missing facts

Section 50(3) is "subject to any agreement in force", so your agreement governs who can license or assign and on what conditions.
The licence or assignment must be in writing and duly executed (section 68).
Agreements and licences affecting title must be filed with the Patent Office; a licence's terms can be kept confidential on the patentee's or licensee's request (section 69(4)).
Record the title or interest on Form 16 (rule 90). A document that is not entered in the register generally cannot be accepted as proof of title (section 69(5)).

The honest answer usually needs someone to look at your actual disclosure, your timeline and the prior art. That is a conversation, not an article.