Hello Soldemar.
While this reply comes 2 months after the initial post but wanted to let you know to keep at it and hope that your family gathering went well. And trust me I can sypathize with your situation.
I married into a full Cuban family and welcoming a strict vegetarian daughter to their clan was shocking. It has been 11 years and they are still pretty clueless. They mean well and as they years go by they make more efforts to accomodate me but it's never usually successful.
Some tips for attending non-veg gatherings:
1. Eat before you go. You can always politely explain why you are not eating and save them the embarrassment for sitting there hungry.
2. Bring your own food. There's no shame in this and it can start a conversation about what foods you eat.
3. If the host is open discuss preparing certain dishes tha are veg friendly. My brother in law always asks me for items that he can prepare for me at his dinners.
4. If you forsee a fight or disaster just don't go.
Keep it up...eating vegetarian is super easy.