It's a subtle point, but this isn't a double-jeopardy issue. Double jeopardy refers to being tried twice for the same crime; in this case, they were tried, convicted, and given a sentence below the minimum allowed; the prosecution appealed the sentence--which happens regularly--and the appeals court found that the sentence was, in fact, below the minimum allowed, so increased it to the minimum. It's rare for that to happen after release, but not impossible.The ranchers in Oregon's charges and sentences didn't fit the "crime", but the issue here is double jeopardy...they already served their time and some liberal judge decided to lock them up again.
Now, I think the whole think stinks on ice, and it sounds like the charges were only brought because the ranchers refused to knuckle under, but it's not a Fifth Amendment violation.