Hi AMS
There are answers to those questions, but I am afraid I am not qualified to answer them......I have been working for BA for under 3 years and haven't yet needed to look into arrangements for partners etc.
Perhaps someone else could help.
Cabin class is dependent on more than just seniority...your role in the company and your reason for travel can also affect which cabin you are entitled to travel in.
An new-entrant crew, you will only usually have entitlement to Club class when on a positioning trip; this basically means the company pay you to fly up to Stockholm for instance, spend the night & work the flight back the next day.