Learn Dutch: Twee weken geleden zijn we wezen zeilen.

This is a special structure for completed outings. When you go somewhere to do an activity and come back, Dutch uses the helping verb zijn followed by wezen and the action verb (zeilen). Because there are two verbs at the end, the expected past participle (geweest) changes into the infinitive wezen.

Does zijn we wezen zeilen mean exactly the same thing as hebben we gezeild?

Not exactly. We hebben gezeild simply means 'we sailed' or 'we have sailed.' Using zijn wezen zeilen adds the idea of an outing: it means you went somewhere to sail and have since returned, much like the English 'we went sailing.'

Why is the word order zijn we and not we zijn?

Because the sentence starts with the time phrase Twee weken geleden (Two weeks ago). In Dutch, the main conjugated verb (here, zijn) must always take the second logical position in the sentence. To keep it in second place, the subject (we) flips to come right after it.

Is wezen considered an infinitive or a past participle in this sentence?

It acts as an infinitive. In Dutch perfect tenses, when a past participle would normally stand next to another infinitive at the end of the sentence, the past participle turns into an infinitive too. This grammar rule is known as the substitute infinitive.