There are a million methods, really. I personally like to use spritesheets of each animation, saved as PNG files. Then I can just cut up each animation in the Animation Importer and easily set the origin points. However, this requires you to know each spritesheet's dimensions, and the frames all need to be the same side if you want it to be as efficient as possible.
Your best bet if you're not intimately familiar with each animation you're being sent is to have your team member make each animation frame as a separate PNG file. That way you don't have to worry about dealing with transparency or trying to figure out frame sizes and things like that. All you end up having to deal with is having a lot of PNG files!