At their age I don’t think you can expect ‘reasonable behaviour’ from them. They will adapt to their surroundings.
Some of what people consider reasonable have changed over the years too. I know it was just an example, but the first thing you mentioned was that the tv stays on when you visit. Are you arriving unexpectedly? If not, then perhaps it is reasonable to expect that it won’t be on, but if you are ‘dropping in’, maybe it is unreasonable to expect the family to stop what they are doing to accommodate you? These days, family life can be busy, with not a lot of ‘downtime’ after work, school and other activities. Letting the children flop in front of TV for a few minutes at the end of the day isn’t seen as the waste of time that it used to be.
As an adult I hate people ‘dropping in’, and resent being expected to conform to others’ ideas of how I ‘should’ spend my time. Could there be something to think about there?
I think that if you enjoy having the children at your house, and they behave as you like them to there, you should maybe relax a bit about what they do in their parents’ home.