All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
As we understood from the question that your husband conditioned the divorce on something which has already occurred i.e. visiting your sister. If this is the case then this is a finalized divorce, and not a conditional divorce, so it is effective.
As for pronouncing three divorces in one word, the scholars have different opinions whether they are three divorces or only one divorce. The details are mentioned in Fatwa 82330. We, in Islamweb, adopted the opinion that all the three divorces. Therefore, your divorce is irrevocable from your husband.
However, as you can see, the issue is controversial, so if you want to refer to an Islamic court then you may do so.
Allaah Knows best.