Why Stan can talk
He's not really a dog- he's a Melmacian, rocketed away from his dying planet as an infant, with no knowledge of his extraterrestrial origins. That would explain his interest in eating cats and ability to write/type, as neither of those things are really doglike traits. As to why he normally walks on four legs, he may be a subspecies that never achieved bipedal status. Ellen and Bennett will find out Stan can talk in the last episode.
Confirmed Ellen and Bennett will find out they've met before.
Tyler and Chloe are adopted, and Avery is a test tube baby
Tyler and Chloe never mention their biological mother, and Avery never mentions her biological father. Tyler and Chloe also quickly refer to Ellen as 'mom' and 'mommy', while Avery is quick to refer to Bennett as 'dad'. Chloe and Tyler also look nothing alike, and nothing like Bennett either. Bennett seems like the type that would adopt (being a child psychologist and all), while Ellen seems like the type who would go with artificial insemination in order to have a child. (She also never mentions an ex-husband or a deceased husband). The other "Ellen James".
The creators of the show chose have Ellen and Avery Jennings keep their maiden name, because "Ellen James" is also the name of a tragic and non-kid-friendly supporting character from "The World According to Garp."