>>48047171>Branch Evo for last stages?Absolutely no, mainly because this wouldn't fix fix, it would just make them obsolete. Besides the finals evos they already have fit thematically as is.
>New/Added Secondary typing?Maybe, but it's unlikely Game Freak would just change their types. If they do I would add Ground for Typhlosion and add Fighting for Samurott. (Fire/Rock could have been an option for Typhlosion since its actually fast enough to make use of its offense potential but H. Arcanine is already Fire/Rock).
>BST reconfigured?Would be cool but that will never happen.
>New HA / moves?This is the best option.
All of them get Ancient Power and Nasty Plot in their movepools.
New Moves for Typhlosion: Earth Power, BoomBurst, Explosion (Maybe Belly Drum)
New Moves for Samurott: Flip Turn, Close Combat, Ice Shard (Maybe Shell Smash)
Decidueye: Improve Long Reach.
Also I'd give them signature items based on their "weapon" that boosts some of their stats (similar to how Light Ball, Thick Club, Leek work for Pikachu, Marowak, Farfeth'd).