They don't like competitive games.
so when playing connect 4 DS1 didn't win every game but he won alot.
SO Grandad changed the game so that there couldn't be a winner.
and DS1 managed to find a way of winning the unwinable game and Grandad was determined that DS1 should get used to loosing as you can't win every time (BUT HE DID WIN!)
So they started having a game of cars - DS1 said ready steady Go and he and DS2 started racing down the hall - and grandad stopped them and said it wasn't about who came first.
AT this point I stepped in.
"Sorry Grandad - the thing is DS1 did win, and it is great that he won, it is also great that he is playing nicely with DS2 a race which he may or may not win"
"but"
"no grandad - no buts - DH and I have NO problem with the boys playing competitive games - one will win - one will loose the balance is there"
at this point he spoke in Chinese to Grandma and they went upstairs and packed and left within 30 minutes - apparently they got vibes that they had overstayed their welcome!
I perhaps should have been more gentle about it but I had listened to him for the last 3 days correcting and disciplining DS1 whilst smiling and cuddling DS2 whilst he was being a PITA.