Well, "time is convoluted" after all... though there are quite a few differences between the characters, and there's the problem of people in the outside world being dead or changed from what they were in DS1 (just look at Gwyndolin).
That said, FromSoft likes reusing assets, characters and storylines in some way... you could argue about reincarnation or that the painted world is on a time loop/different timeline to the rest of the world. Plus, we never meet the painter Ariamis. It could very well be that, while the Base Game DS3 plays in the future (Irithyll is built on Anor Londos ruins, Gwyndolin is dead etc...), the Painted Worlds are on a reverse, looped or simply different timeline: that Ariamis and Priscilla from the first game are the future, while Ariandel is the painted world of the Past, with Ariamis yet to have been painted.
It's really complicated and messy, though, make of that what you will.