וַיֹּאמְר֗וּ שָׁל֛וֹם לְעַבְדְּךָ֥ לְאָבִ֖ינוּ עוֹדֶ֣נּוּ חָ֑י וַֽיִּקְּד֖וּ וישתחו [וַיִּֽשְׁתַּחֲוּֽוּ׃]
他們說：«你的僕人我們的父親平安，他還活著。»於是他們低頭下拜。
Rashi
ויקדו וישתחו AND THEY BOWED THE HEAD AND PROSTRATED THEMSELVES — in recognition of his enquiry regarding their welfare. The root קדד denotes bowing the head: the verb שחה in the Hiphil denotes prostration upon the ground (Megillah 22b).
Ibn Ezra
They bowed (vayikdu) … and prostrated. They lowered their heads (kadkod) to the ground after having already prostrated themselves.
Radak
ויקדו וישתחוו, when they prostrated themselves this was with the intention of making an obeisance to their father after whom Joseph had inquired (although outwardly, this was not noticeable).