First of all, a lot of parents will tell you their children are way better behaved when they're with grandparents or other adults. Strictly speaking, I believe that holds true for most of us adults as well. To me, this only says that the relationship with the grandparents is not such that the child feels safe enough to display all his big feelings for. I don't find that problematic in itself, but I also don't think parents should strive to achieve the same relationship. A child who has no close adults to be upset with should not be mistaken for a contented child.
Transitioning from one activity to another is a rather classic conflict area. Seen from the perspective that such transitions (getting up, leaving for school, coming to the dinner table, going to bed) is almost always the case of a parent interrupting a child in the middle of something, to push their own (however well motivated) agenda, this is also an unsurprising pain point. I think there may be ways to alleviate those situations. Generally, it is helpful to transition gradually. Lean in and engage with what the child is doing, so that the transition from being immersed in, say video games or TV, to interacting with the parent is seamless. Come in early enough to give the child a chance to find a smooth exit from their current activity, rather than stopping in the middle of their tracks because you command it. Be it reaching a save point in a game, or being able to finish a particular thought. Just as most of us would have a problem with having to drop what we were doing at work in an instance because someone decides we must leave immediately.
There's likely no quick fix for the child's violent behaviour. I would advocate seeing past that on the heat of the moment, and make sure the child is (and feels) seen and heard in his upset, and that you defer until later the discussion on what's acceptable behaviour during an upset. Always use a personal voice, and tell the child that you're hurt or sad when they are violent, don't just lay down rules about "this is the range of allowed behaviour", as such rules are generally less relatable. In general, though, my impression is that upset children need to be listened to more than they need to be told things.