▲only have to do sth 的意思是“只要（做……）即可”，言其简单，言其轻，言其容易。如：
He’ll take you home—you only have to ask. 他愿意送你回家——你跟他一说就行。
If you want me to leave, you only have to say the word. 你要是想让我走，尽管说出来就是了。
We only have to read the labels to know what ingredients are in foods. 我们只要看一下标签即可知道食品的成分。
Any time you want a babysitter, dear, you only have to ask. 亲爱的，你什么时候需要人帮忙照看孩子，只要开口说一声就行。
▲just have to do sth 的意思是“还只得”“还只好”，言其无奈，言其被迫。如：
We’ll just have to live with the problem for now. 目前我们只得在这个问题上妥协。
We’ll just have to sit it out here until things improve. 我们只好一直在这儿熬到事情有转机。
No decision will be made until next year, so you’ll just have to wait and see. 要到明后才会作出决定，所以你只好等等看了。
I hate having my wife’s parents to stay, but I suppose I’ll just have to grin and hear it. 我讨厌我的岳父母住下去，但我只好苦笑着忍受吧。
▲你的两个句子：
Carrying the bags upstairs is half the battle. Then we only have to unpack them. 把这些袋子搬上楼就基本上大功告成了。接下来的我们就只要解开袋子就行了。
Our views on this matter are so different—I think we’ll just have to agree to differ. 我们在这一问题上的看法分歧很大——我想我们只能保留不同意见了。