The translation you choose was presumably influenced by the Biblical narrative that Mary's father's name wasn't Imran. So, they translated in a way to accomodate that and say Mary's mother wasn't the wife of Imran, but just a woman from the House of a man called Imran.
So, the intent of the translator was not to say Imran had multiple wives but to say that Imran wasn't actually her husband in the first place. He could have been, apparently, an ancestor or patriarch of the family.
The plain words of the Arabic are: امْرَأَتُ عِمْرَانَ
It does not necessarily show an indefinite article. It can simply be translated as "the woman of Imran" hence "the wife of Imran."
Similar construction can be seen in 28:9, where Allah says "امْرَأَتُ فِرْعَوْن" (the wife of Pharaoh) where the only difference in the Arabic construction is that the name Pharaoh is substituted for Imran.