descend from vs be descended from

Yes, those are all okay. The difference is that descended is functioning as a subject complement / participle adjective, while descend is an intransitive verb here. (Either way, there is no passive voice construction possible.)

The Oxford Enlish Dictionary (login required) does not go so far as to label descended as an adjective in this usage, but it does note that it acts like one:

descend, v.
a. intransitive (in the perfect). to be descended (from, †of): to come or derive from a particular progenitor, ancestor, or ancestral stock; to be a descendant of.
_{Originally the perfect tense formed with be, but now felt to be a predicative use of the past participle with be.
[selected examples]
1944   W. S. Maugham Razor's Edge iii. 116   I am descended in the female line from the Count de Lauria who came over to England in the suite of Philip the Second.
2004   Focus Feb. 44/2   Every human on the planet is descended from between one and seven women who were part of a group of perhaps 200 individuals a few million years ago.}

Collins goes right ahead and calls it an adjective:

descended
_{ADJECTIVE [v-link ADJ from n]}
A person who is descended from someone who lived a long time ago is directly related to them.
_{Anna is descended from pioneers who settled in Colorado in 1898.}