will my brother do a lot of time if he is charged with intoxication assault, but his blood drug/alcohol test shows he was below the .08%

It depends on what the blood test results are. They test for more than just alcohol. If there were prescription drugs and/or illegal drugs, the fact that his blood alcohol content was below .08 will not matter, in terms of whether he will be prosecuted. However, be sure he hires a very good DWI lawyer to represent him. Alcohol in the blood should not be looked at the same way as drugs in the system. Mere presence of drugs, or the metabolites of drugs, may not be enough to convince a jury that he was legally intoxicated.