Hans was born April 1997, Marie January 1998, and Heidi February 2001. So Hans is 9 months older than Marie. Current point in the story (March 2009, in Chapter 230) has them at ages 11, 11, and 8 respectively, as Marie just had her birthday, but Hans hasn't had his yet. In the image above, it's about September 2008, at the start of their first year together in Pouncefield. At that point their ages would have been 11, 10, and 8, respectively, for Hans Bernerholdt, Marie LeChow, and Heidi Bernerholdt.
Marie's mom, Miss Cheri, was born December 1984, but looks almost the same age as Marie, because she stopped developing physically at about age 12, just a few years after puberty hit for her. We don't know yet, in the stories, if Marie has the same genetic flaw as her mom for that arrested development.
Hans was born April 1997, Marie January 1998, and Heidi February 2001. So Hans is 9 months older tha