The question of starting for the United States was discussed from day to day in the family council. It was finally resolved (that主语从句)we would join relatives already in Pittsburgh. I well remember （that 宾语从句） both father and mother thought (引导宾语从句的that连词省略)the decision was a great sacrifice for them, but that "it would be better for the two boys."

参考译文：那几天的家庭会议一直在讨论动身去美国的问题。最终我们决定去投奔已在匹兹堡落足的亲戚。我清楚的记得我父母都认为这一决定对他们来说是重大的牺牲，然而“对两个孩子会有好处”。

1、be resolved是被动式还是that we would join relatives already in Pittsburgh was resolved

解答如下：

你的理解是正确的，that为主语从句，it为形式主语

2、that "it would be better for the two boys."是remember的宾语吗？如果不是that在这什么意思？这个从句什么理解

解答：

that decision...but that作谓语动词thought的宾语
（备注：动词后接多个宾语从句，第1个that连词可省略，第2个that能省略）