Continuity mistake: Dom escapes his crew by crashing through a flower stall, leaving flowers and other debris on his car. Just seconds later we see his car again and it's pristine - it looks like it's just been washed.
Continuity mistake: Dom dives out of the burning car and lands on the concrete sidewalk, but then a different shot shows him getting up from the road. No way he could have reversed all that forwards momentum and rolled backwards.
Continuity mistake: As Dom escapes the grappling hooks, the cars get wrecked. He crawls out from his car and the silver briefcase is within arm's reach, right next to double yellow lines. Only problem is, in the earlier shot from above, he crashed nowhere near lines like that, and there was no briefcase there either.
Continuity mistake: The extras behind the guy Dom's cousin is indebted to keep changing in different shots.
Answer: Well, we know that Owen Shaw was once an SAS soldier. Deckard Shaw has a file in this movie that reveals he saved a team he was part of and saved some hostages in the past. When Deckard Shaw refused to do the job Cypher wanted him to do in Furious 6 to steal the nightshade device, Cypher then went after Owen Shaw and convinced him to do the job. Cypher is the true mastermind behind everything that has happened in Furious 6, 7 and 8. So, maybe the Shaw brothers were good guys at a time before Cypher came along.