Most of the Brawl modding community is not this professional in animating, let alone modelling. The only group of people who would be able to do something like this would be the Project M team and clearly that would be a waste of their time seeing as they have their own things to work on.
There is simply no way these videos are a Brawl mod. The people would have had to meticulously recreate all of Bowser's Smash 4 animations, replicate the exact knockback/hitboxes and behavior of Bowser's firebreath (it's shown in the video and behaves exactly how it did at E3 and in the videos we've seen of Bowser) as well as any other possible move they'd use, make the Smash 4 models of other two veterans featured in the video on Battlefield, and do all of that while modelling and animating a completely new character that can't even reuse animations from other characters.
If Mewtwo took the Project M team a total of like 700 hours to animate, something like Bowser Jr. to animate this well would take even longer.
The point is: these are not Brawl mods. You're in denial if you think they are.