We can see that the ancestors have different eight letter names than their pre scratch selves... Why did they change their names?? Are they still the same people?? Is the eight letter thing trolls do once they reach adult hood or something??

They’re not names. They’re titles. A lot of them specifically, in fact, are given by Mindfang, which may mean the 8-letter naming convention is just her using her Quirk. Like, seriously, Expatri8 only works for Mindfang, and with Scratch, while The Condesce/Baroness does follow the rule, Her Imperious Condescension and The Grand Highblood definitely don’t. Psi’s title, too, only fits if you use the Psi symbol at the beginning and count it as a single symbol. So yeah the Ancestor Naming is all titles, and very messy.