Hi Greg,

Yes, 2 potatoes in a 5 gallon bucket should work fine unless you're using whole potatoes that are large, and then you may want to go with just one. 

Most red potatoes are determinate, which means they will grow in an even layer at the roots and do not require hilling.  Because of the smaller space, I recommend planting them about midway in the bucket and covering them with a few inches of soil.  You could also stagger the planting depth so they don't get too crowded.

Once they start to grow you can add more soil to the bucket so the potatoes grow deep enough in the bucket that they won't be exposed to sunlight and turn green.