The mother of the grandtwins informs me they probably won't be toilet-training prodigies.

Interesting family fact: My wife spotted this one.
She and her Minnesota brother each have two children. The elder sibling of the each family resides in the Denver, Colorado, metro area about 15 minutes apart. Each became a parent in 2010.
The younger sibling in each family resides in the Twin Cities also about 15 minutes apart.

Aloha, Julie.