No. Ons can mean:
In your sentence, it clearly means we, because it is followed by the verb twyfel.
Afrikaans usually uses:
So:
In your sentence, this is not a condition. It is a whether clause, so of is the correct word.
Because of introduces a subordinate clause, and in Afrikaans the finite verb often moves to the end of that clause.
Compare:
This is a very common Afrikaans pattern after words like dat, omdat, as, wanneer, and of.
Because moontlik is being used after the verb is, so it is a predicative adjective. In that position, Afrikaans adjectives normally stay in their basic form.
But before a noun, you often use the inflected form:
So:
Usually, no. Afrikaans verbs generally do not change form for different persons in the present tense.
So you get:
That is much simpler than English. The verb twyfel stays the same.
Yes. Dit here works like English it.
Just like in English, the sentence needs that subject pronoun. You would not normally leave it out.
So inside the clause of dit moontlik is, dit is the subject of is.
Yes. Ons twyfel of dit moontlik is is a normal and grammatical Afrikaans sentence.
It sounds natural in both speech and writing, and it uses very standard patterns:
So it is a very useful sentence model to learn.