bodies
Bog bodies are unique; well-preserved corpses that, unlike mummies, have not undergone burial wrappings or rituals. They may have been sacrifices or were subject of execution.
Again, they are very well-preserved. The peat in the bog tans their skin so they appear brown or rusty in color. The hair usually remains. They are emaciated, but features still hold. They retain their internal organs. The bones generally dissolve.
Sean and Conor will be played by actors. It will be necessary that those cast be extremely thin.
Jack will be portrayed by a puppet, due to the fact that he is particularly broken-down (jawless, missing his bottom half and an arm).
Makeup
There aren’t many bog bodies to cinematically reference, as there aren’t many movies about bog bodies (save for a few early-aughts slasher films).
Jack Goodman from American Werewolf in London is closest example of what I’m looking for for Sean and Conor’s makeup (and demeanor), especially his look towards the end of the film. The work is very practical and gory, but played a light-heartedly. The zombie makeup on the below slides should also be considered for reference.
Sean, Conor, and Jack should be unsettlingly made up, but sweetly portrayed.