Translation:I am happy that my family has passed by to see me.
être passé = to pass by/to come visit
se passer = to happen
"(il/elle) soit passé/e" is the subjunctive form of "être passé"
"il se soit passé" means "it would have happened" (kind of hard to translate out of a sentence though, as subjunctive form does not really exist in English)
I am happy that my family had come by to see me. This was marked wrong. Compare it to the answer that was accepted. What is the problem?
This whole lesson on the subjunctive is horrible.
It is taking the longest time to get through it, because there are so many answers that should be accepted that are not, and so many answers that were accepted before that are not now.
This whole lesson needs to be scrapped and started over.