It was finally resolved that we would join relatives already in Pittsburgh. 

【翻译】我们要和已在匹兹堡的亲戚团聚的事最终解决了。

1. It was finally resolved that we would join relatives already in Pittsburgh. 

= That we would join relatives already in Pittsburgh was resolved.

2. It（形式主语）was finally resolved（被动语态或系表结构均可） that we would join relatives already in Pittsburgh.（主语从句）

“It is + 过去分词 + that从句”结构举例：

(1) be acknowledged  承认

It is acknowledged that geopolitics has influenced the foreign policies of Islamic states more than religion

(2) be admitted 承认；赞同

It is admitted that the speaker submitted inaccurate information.

(3) be agreed 达成一致；一致同意

It is agreed that the secret room should contrast in decadence with the stark environs of the room outside and the rest of the museum.

(4 be accepted公认可接受；认可

At some point it is accepted that we are not all bad guys.

(5) be believed 认为；料想

It was believed that the winner was favored by the gods, and so brought honor and glory to his village.