这三个词都是两个人的意思，可在用时确实有不同的地方。
“两人” 就是 “两个人“，”个”这个数量词是可有可无的；而“二人”是不能有数量词的；“俩人”也不能有数量词，较“两人”和“二人”更口语化。
这三个词，在很多情况下可互换，可是有些时候是固定表达，而且不可互换，比如：二人转，二人世界，判若两人，等。
As a professional Mandarin instructor with almost two decades worth of teaching experience in American schools, I came to recognize how language-learning in a school setting is only one step in the long journey of acquiring a foreign language. I felt a need and urge to bring my profession beyond school, and I believe professional teaching should be accessible to anyone at any point in their life. It is with this belief that I founded MAD Mandarin LLC in 2018 with the goal to incorporate the latest teaching methods with my own innovative approach of Mindful-Active-Dynamic to positively achieve the best language-learning results.