When do dj and steve start dating
His father is absent because his father is future-Jesse (Stavros? I think evidence points to Alex being Cousin Steve, drawing primarily on the episode "Yours, Mine and Ours" wherein Alex is sick and Jesse and Becky imagine the effects of their different parenting styles on the twins.
He lives "in Baltimore" because he, unlike his brother, is not a permanent resident in the past, so he must claim residence sufficiently far away to avoid suspicion.
Consider: (a) Cousin Steve was sicklier in his youth: glasses, acne, braces, weak, scrawny, etc. (b) Cousin Steve wants to spend time with the guys, perhaps making up for a weaker relationship with his father in his childhood.
Unlike Cousin Steve, there's nothing that forces the conclusion that Boyfriend Steve is a time-traveler.
Cousin Steve has no possibe parents that would make him DJ's cousin.
Her father has one sister who is childless later in the series.