We are US citizens holding Ecuadorian residency cards living permanently in Ecuador. We want to travel to Columbia first then Cuba. Can we do this? Or do we have to travel to Cuba only from Ecuador?
You can fly to Cuba via any airport with service to Cuba.
The restrictions on Americans is in regard to what you do once you are there. US citizens are limited to 12 specific travel reasons, many related to family and business, but as few, such as supporting the Cuba people, Humanitarian, Education are being used as "tours". The most common being a "People to People" tour, an itinerary with some cultural or educational exchange component.
The fact that you are permanent Ecuadorian residents does not relieve you of this, as you still travel under US Passports. And most tour operators in Cuba are aware of and abide by those rules, as they want to benefit from a new potentially huge market.