The oldest will just have to watch what is also suitable for the 4 yr old.
So my oldest still watched Thomas, when he was 7, and Diego. They started watching power rangers, ben ten etc when the youngest was about 4 or 5 though.
They are phyiscal boys, they love shooting ( nerf guns), fighting (judo and karate) and stuff like rugby. They watch quite scary and violent stuff, IMO ( we only have freeview though) like Harry Potter, Indiana Jones, Starwars.
BUT, and this is important, they are not at all violent or agressive with eachother, or with friends. Never hurt anyone, do not get into fights.
Whilst they love action hero roleplay, and "bangbang you are dead" games, they are complete softies in real life, and very gentle.
I am not a psychologist, but I think that boys ( and girls? Do not know about girls as am mum of boys) like to roleplay violent and action games, but that does not mean anything negative about their character. I know my nieces play quite violent games with their barbies too!
My oldest is 10, and loves all the martial arts, nerf guns and action movies, but he also says he wants to be a vegetarian and a buddhist as he thinks even killing headlice is wrong, and why is there no way to get rid of them without killing them.
Just a tiny example. But IME, watching Power rangers and stuff does not necessarily lead to violent behaviour.
Also, I do remember both boys being a bit trickier around age 4 and 7, do not know if it is a hormonal thing, or psychological though. But 4 yr old boys and 7 yr old boys are quite full of themselves, lots of bravado...which then mercifully fades again.