Wayra;
I have been involved in forming a Pilots association and I am willing to help.
However, I am not quite certain what your question is. In my experience, the association would have one set of articles of association and bylaws that would would govern all members irrespective of the rank they hold at work.
Further, while there may be some specific duties & responsibilities for Captains or F/O's, the conditions of employment ought to be the same, albeit at a different rate, which in any event will be one of the hardest things to negotiate with your employer once the association has been recognised as the sole bargaining agent for all Pilots at your company.
I would also suggest that you visit
www.ifalpa.org and perhaps contact them for assistance. I have several friends Mexicana and Aeromexico that are very active in Ifalpa through their home association "ASPA de Mexico". Naturally they all speak spanish which may be of further assistance to you and your coleagues.
Good luck to you!