No, both sentences are awkward.
The first should read:
We had been dating for three years before we married
NOT before we had married.
That's to say that the PAST PERFECT CONTINUOUS tense (relating to an earlier period - dating) is followed by the PAST TENSE (relating to a later point in time - marriage date).
And the second:
I have been studying English since I met Sally
I have been studying English since meeting Sally.
Here you met Sally at some point in the past (PAST TENSE) and since that point you have been studying English (PRESENT PERFECT CONTINUOUS), taking you up to the present time.
Both sentences are written in the ACTIVE VOICE. Trying to turn them into the PASSIVE VOICE (English had been studied by me....etc) simply wouldn't work.