The issue here is the treatment of driving a bike drunk and driving a car drunk as equivalent in the eyes of the law. They're not the same for pretty obvious reasons, but they are in the eyes of the law.
Lets say the Gaudreau's were driving a car drunk, followed the laws of the road and were driving perfectly while doing it, then Higgins who is less drunk, crashes into them and kills them. The Gaudreau's impairment had absolutely nothing to do with the crash (as is likely in the bike scenario as well), but their level of intoxication absolutely would play a role in charges and sentencing for Higgins in the case where both are in cars.
Pretend they were in a car, not on a bike. It makes no logical sense, but that's pretty much how it needs to be looked at legally.