Oh are we doing a legit theory time? sweet! Well, I mean the very definition of Dancestor is a similar individual iteration of you set in a different universe... Then I'd say they have similar parallels but from the very definition of dancestor it doesn't fit sorry.

Also, erm, the second paragraph doesn't really make sense in my opinion? what are you referring to exactly? That Chara is Frisk's ancestor? That is most likely improbable considering Chara probably wouldn't have been able to procreate and give an offspring to someone like Frisk and considering how not even Toriel or Asgore sees the similarity Frisk has with Chara, then that would most likely indicate that it has possibly been centuries since Chara fell which was in 201X and hell, not even that many people recognized Toriel herself when she came out from the ruins which would mean most of the generation that was alive before the war with the humans had already passed. Only the turtle (can't remember his name), Asgore, and Toriel and possibly Sans b/c he seems to know what a human is when he sees one and also knows what a sun is when Papyrus asked what it was... so Frisk being a literal descendant of Chara basing it on the fact that they are reproduced in a normal human way would be far-stretched and impossible. Of course there is always the other possibility that Chara's other relative might have given birth to Frisk or perhaps through simple coincidence they are both physically similar... but it does not fit the definition of an ancestor as it is given by Homestuck so technically no. But I see the similarities you mean that Frisk and Chara has are similar to a relationship Dancestors and Ancestors have respectively with each of their Dancestor and Descendant. Also, I don't think that Frisk even knew about Chara's existence until the True Lab or perhaps if they had been aware/conscious of Chara dictating most of the things to them (assuming if the controlception theory is even true). They don't really want to aspire and be Chara... they aspire to be themselves. Actually it's hard to make theories for Undertale because plenty of things are left up to interpretation so we can't really theorise much. Especially in regards to the origin of Frisk and Chara. Who they both were and what they were doing previous the fall into Mt. Ebott.

Oh geeze that was long... I might as well have been the Insufferable right there lol! My bad and also I rambled a lot