Not completely. Schools of origin might be, but the timeframe is not. The starters were not accurate based on the state listing. Also, two are sons of Althoff grads - not outlandish to make that move. Also, the baseball coach came from Granite - not surprised some of his kids followed him. West to Althoff happens all of the time - and vice versa.
Let us address the big two - Dowell and Dierre. Both came after freshman year. Dowell is a devout man of God. His older brother went to Althoff and was coached by the previous baseball manager, who happens to be the Mayor of Sauget, BTW. Cahokia High, the be plain, got very bad. There are more shootings in that village than East Saint.
Dierre's family moved and established roots in Belleville. Born and raised in Centralia, his family moved to STL late in grade school. After seeing that life, they too wanted to escape the violence for a better setting for their children. A few kids came from Ritter for the same reason and already lived in Illinois.
It does look suspicious when generations live on the same plot of land and sometimes the same house all of their lives. But the reality is, there are transient families down here.