i make a lot of Rodrina edits using Devon Bostick to represent Rodrick Heffley since he is the most well known actor to play the character. (sidebar: Poor Charlie Wright was screwed of the opportunity with that fuckass bob and i hope everyone that sent racist death threats lives long miserable lives and dies equally as long and miserable. yall fucking suck)
despite this, my pinterest board and headcanon is Nat Wolff (alex interchangeably if i'm being honest). Especially when we have a perfectly good little brother (Alex Wolff) for Greg. they're both in several films and are musicians so there's lots of references of them playing together, which fits my narrative that Rodrick teaches Greg to play when they get older and become closer. they just fit my young adult heffley brothers vibe.
Manny hasn't played a crucial role enough for me to create a solid headcanon so he's just a vague concept of a person. would've been too convenient if that had a third brother that was roughly 10yrs younger. IDK maybe Thomas Barbusca or some young actor that has 'asshole little brother' vibes.