Sitting watching TV wont help them they want to be active, parks ,gardens, games.they fight because they are bored and its probably the older one who starts it. they dont need discipline for this they need participation from parents ..get dad involved aswell.. its summer ..ball games are fun .
Sounds like they need a lot more physical activity - kids who don't just "sit and watch TV" are a great thing. Do you take them places they can run everyday - parks, or large buildings where they are allowed to run up and down stairs and explore?
That would probably solve most of the fighting. Also, the book "Siblings without Rivalry" is good with suggestions to keep them from squabbling.