EK has been interviewed by the Sun about his brother. I can't post the link because I've got the paper copy but it's a good read. Apparently Ron used to chase Erwin with a pool cue when Erwin beat him.
The main points: Ron always had fire in his belly. Erwin was always the calmer brother. They had a real passion for football from a young age due to their father Martin. The South Stand at FC Groningen is named the Koeman Tribune in their honour (Martin, Ron and Erwin) Their father died last year of a heart attack aged 75 and Erwin is sad that he didn't get to see the work they are doing at Southampton. But he would be proud of both of them. Ron and Erwin managed to get an unfashionable team into Europe before (Groningen) as players. Why can't we do it as management? He asks. Erwin's son Len will be at the game today. Finally he is confident of beating City today.