Is there a difference between "ascendants" and "ancestors"?

Without noticing myself, I've mixed the use of "ascendants" and "ancestors" in some documentation I've written.

In an arbitrary hierarchy (of either people or things), what would be the most correct term to use, to describe my parent(s) parent(s) parent(s), etc.?

That is, descendants would be my children, their children, and so forth. In the exact reverse order, would ascendants and ancestors be interchangeable, or would one be preferred over the other?

Both TheFreeDictionary.com and Dictionary.com lists ancestor as a synonym of ascendants, though neither precisely defines it in the context of a hierarchy per se.

Ascendant does have the meaning you use here, but it is rare, and many may not know that sense of the word, so you should favour ancestor.

(The other senses of ascendant do also have descendant as an antonym too, so if you look up the antonym of descendant you may find ascendant cited for that reason more than for this rare sense).

I think what you mean is antecedent vs. ancestor. I am not sure if ascendent connotes the meaning you have in mind, but the two others I suggested would be interchangeable in some contexts. However, in your specific case ancestor seems to be a better fit.