Requirement for "qui" in case "dont" + number is followed by a conjugated verb

Question

This point has been already raised in an answer to a previous question but has not received any attention. So would like to pick it up again.

I have two grammar books containing examples with "dont" and numbers which do not state this requirement for "qui". For brevity I will just cite one of them:

"Grammaire Progressive du Français B1 B2", 2019, p.116:
"Ils ont trois grands enfants dont deux sont médecins."

So my assumption is that "qui" is not required, if the "number" is the subject of the next sentence.

Accepted Answer

In my understanding, both versions are possible with the first one being a bit less formal:

Ils ont trois grands enfants dont deux sont médecins.
Ils ont trois grands enfants dont deux qui sont médecins.

And there is an even more concise version:

Ils ont trois grands enfants dont deux médecins.

Answer

Salut Christian,https://www.lawlessfrench.com/grammar/relative-pronouns/I think the above link may offer further explanation."Characteristics of relative pronouns. Connect relative and main clauses can be subjects, direct objects, or objects of a preposition impersonal and therefore invariable (except lequel)Are required in French, though they are sometimes optional in English"I have copied the above for further clarification from that link  -- I hope that this may clarify the grammar for you.Bonne journéeJim

Answer

@Jim @Chris: Thank you for taking the time to answer!

@Jim: The linked page does not help answer my question. Also, I am not reasoning by comparison with English but with examples from other French grammar books that contradict what is stated here as a rule.

@Chris: After now also doing some googling texts from French newspapers, it really seems like both versions even with other verbs than être can be used (e.g. "Ils ont trois grands enfants, dont deux habitent à Paris."). I would be curious, if you have any reference about the version with "qui" being more formal.

Answer

No, I don't have any reference for that except that over the years it's acquired this flavor by assimilation. This can only be decided definitively by a French native speaker.