Regarding the expired Brazilian passport, I wouldn't count on that to avoid anything. I traveled to Brazil once with an "autorização de viagem" because my Brazilian passport was expired and the Brazilian Consulate wouldn't issue a new one in time. It was never a problem for me to leave Europe, since I have an European passport too. When I arrived in Brazil, I proactively showed the man on the border that the Brazilian passport was expired and that I had an authorization. I'm pretty sure he wouldn't even notice. But even if I didn't have the authorization what would he do? I am a Brazilian citizen. Where would he send me to?
Just another thing, most Brazilian people understand spanish very well, with no study at all. And also speak well enough to comunicate easily. Portuguese and spanish are very similar, but Portuguese has more sounds than Spanish. So, Spanish is almost like a "bonus" for portuguese speakers. It's not that easy the other way around. Spanish speaking people will not understand portuguese that easily. So, if this is the case that he could be trying some kind of "kidnapping arrangement" in Mexico, language wouldn't be a problem.
I'm very sorry for your situation. I would go for all the proactive advices you received in this forum. Don't be naive, get a lawyer, take all actions.
I would also dare to give one more piece of advice. Make a network of friends, count on them for personnal support for you. They can help you to stay strong when things get ugly, which probably will happen, let's face it.