@IClaudine police are asking for videos from the public too about that. So far , I haven't seen any, I don't know if they have received any or if they will be released.
I can only repeat what the news say and the police have stated, so I can't guarantee the full accuracy of this.
Basically, an incident happened between their mum on the flight , and again at baggage claim(police are also asking for any videos of this). When their mum came out she told them what happened and pointed a man out. An incident occurred between these two and the man (some news sources report another incident at Starbucks). This initial confrontation is why the police attended and why they (presumably) went hot straight for the brothers to arrest them.