I know a few kids like that, although thankfully not mine. Having said that mine do fight and show defiance from time to time so I think the behaviours are normal, but acting like that all the time is what's not normal iyswim.
Exactly what Traveller said. Showing defiance is kind of normal as they "Test" the boundaries - mine tend to do it more at their grandparents house's as they try and see what they can get away with. I suspect some of it is "for show" being at your house and in a different environment. Doesn't make it right but it also doesn't mean they are like that all the time.

Wrestling and karate chopping is kind of normal especially amongst boys/brothers/cousins....I wouldn't be too worried about that. I would be worried if escalated to punching tho - that is completely different type of behaviour that warrants addressing.