Why did they need to say, "We will give our daughters to you, and we will take your daughters"? Chamor already said so!
Ohr ha'Chayim: This was part of the Chochmah. They showed adamancy about the stipulations, unlike one who is insincere and pardons his rights to entice the other to agree.
QUESTIONS ON RASHI
Rashi writes: "We will take your daughters..." Rashi points out that Shechem and Chamor had implied (34:9) that the prerogative of selecting brides would be in the hands of Yaakov's family; and they responded in kind. To their own citizens, however, Shechem and Chamor switch terms, and put it at their own discretion, saying, 'we will take their daughters, etc.' (34:21). Is there any other way to interpret this?
Gur Aryeh: Yaakov's sons placed a condition upon Shechem - the agreement would be valid only if they circumcised their males. At this point, they had not done so; and therefore the discretion was certainly in the hands of Yaakov's sons. When Shechem and Chamor spoke to the local populace, they were emphasizing the benefits that Yaakov's family could bring for the city. They had not yet mentioned the stipulation to circumcise (34:22). There is no need to infer, as Rashi does, that Shechem and Chamor were devious towards their own people.