"We had known our mother."
Translation:Nós tínhamos conhecido nossa mãe.
I cannot avoid the feeling... but this tense asks for a time reference.
"We had known our mother by the time we left the orphanage." = "Nós tínhamos conhecido nossa mãe na época que saímos do orfanato"
No, the translation is wrong. The simple (or synthetic) pluperfect would be "Nós conhecêramos nossa mãe."
But nobody talks like that, you'll only see it in written form. In spoken form, the compound pluperfect (just like in English) is used. The compound pluperfect is formed by using either the auxiliary verb "ter" or "haver" in the imperfect past tense + the other verb in the past participle. So the phrase would be "Nós tínhamos/havíamos conhecido nossa mãe".
Thank you erudis for revealing to me that the simple pluperfect is not used in speech. I never understood why there were these two alternatives and what was the difference.
Not the same meaning. It would mean "we have been knowing our mother" (like if she was unknown and is getting to be known gradually)
This is one of those cases where the "have been -ing" translation doesn't work well, at least if you translate "conhecer" as simply "know". This page explains the technicalities: http://www.perfect-english-grammar.com/stative-verbs.html.
Of course, your idea of what "Nós temos conhecido nossa mãe" means, that is "We have been getting to know our mother" fits the pattern provided "conhecer" can be translated as "to get to know".
"We had known our mother." is Preterito mais-que-perfeito of "to know". This tense has not been covered by the skill tree, and it does not translate to Pretérito imperfeito.
I wrote Pret. mais-que-perfeito "Nós conhecêramos a nossa mãe" Which I believe is correct. I got this from http://www.conjuga-me.net/verbo-conhecer
Perhaps the task test should have been "We knew our mother.
The skill tree is mistaken about the names it gives to the Portuguese tenses.
This "tínhamos conhecido" is the "pretérito-mais-que-perfeito composto". But the tree calls it "past perfect" because it matches the English's past perfect (both structure and meaning).
So, it is covered indeed, just with a wrong name.
About the "pretérito-mais-que-perfeito" (conhecêramos), it has the same meaning, but as Erudis said, it's very rarely used.
See more about Portuguese tenses involving past: