A little correction
Hello, Ryuk san. I'm Hirashin, a Japanese man.
I'd like to write something about 「私は」山で日本人の男と女を行きました。
If you say （私は）山へ日本人の男女と一緒に行きました (watashi wa) yama e nihonjin no danjo to isshoni ikimashita, it means "I went to a/the mountain with a Japanese man and woman (/with Japanese men and women).
山で usually means "in/on the mountain(s)", such as 私は山で道に迷った watashi wa yama de michi ni mayotta, which means "I lost my way in the mountains".
If you are to use 行く, you should say 山に or 山へ. 山に行く or 山へ行く would be fine.
And there's one more thing you should be careful about.
男 and 女 are not polite terms. If you say 日本人の男と女と一緒に山へ行った, it sounds arrogant. You should use 男女 (danjo), 男性と女性 (dansei to josei) instead.
> I went to the mountains with a Japanese man and woman (weird example I
> know, but it's textbook material
You mean the sentence is from your textbook? If so, maybe you should not use it.
Feel free to correct my English if needed.
Hope this helps.
Hirashin