Commentary for Genesis 34:9

בנותיכם תתנו ואת בנותינו תקחו לכם, the sons of Yaakov, on their part made intermarriage something that was in their honour, “i.e. to give and to take.” When Shechem and Chamor presented this proposal to their townspeople they reversed it to make it appear as if they were the ones bestowing honour, when they said: “we will take and we will give.” (verse 31) They did this in order to seduce their townsfolk to submit to circumcision.

והתחתנו אותנו, the word אותנו here means the same as if the Torah had written either עמנו or בנו, “with us.”