Family, and character development on Star Trek: The Next Generation

Data did not develop much throughout the series. It was in Generations where he did. Wesley developed in the beginning, and we see plenty of that, but then he was "put on a shuttle".

Riker's development was just the beard (because he was getting visibly older at one point), and that over time, his midsection got softer and softer.

Troi did develop, albeit slowly, and we get to see her in different settings; her role as "Major Rakal" in "Face of the Enemy" stands out. Oh, Deanna's fab mom Lwaxana, a dead father and a dead sister she didn't know about.

Throughout TNG's run, Worf got the most development of all people, as we see him promoted once or twice, find a mate, have a child later on, and we get to see his brother Kurn, and his (Worf's) adopted parents.

Data had just as much: a grandfather in Dr. Ira Graves, a father in Dr. Soong, a mother in Juliana Soong Tainer, his late daughter Lal, an evil brother, and B4, presumably a half-brother.

Compared that, we only saw Picard's brother and maybe nephew; Riker had an estranged father, a dead mother, and a clone brother; Dr. Crusher was the widow of a dead husband.

Tasha had a sister whom we saw only after Tasha's death, and her alternative-universe self got into the prime universe, and had Sela.

Let's not forget Ensign Ro. Her life seemed in some ways to reflect that of Tasha. Ro eventually left Starfleet and joined the Maquis.

O'Brien married, and he and Keiko had a daughter.

In the end, I could posit, that TNG had character development, but it was slow for all characters, and there were few who had more than even the primary characters.