וַיֹּ֤אמֶר בְּנֵי־גָד֙ וּבְנֵ֣י רְאוּבֵ֔ן אֶל־מֹשֶׁ֖ה לֵאמֹ֑ר עֲבָדֶ֣יךָ יַעֲשׂ֔וּ כַּאֲשֶׁ֥ר אֲדֹנִ֖י מְצַוֶּֽה׃
迦得的子孫和流便的子孫對摩西說：「你的僕人們必照我主所吩咐的去做。
Rashi
ויאמר בני גד AND THE CHILDREN OF GAD SAID, all of them as one man (ויאמר is the singular form of the verb, whilst the subject בגי גד is the plural; cf. Rashi on Exodus 19:2 s. v.).
Sforno
עבדיך יעשו, the part of the condition which involves our being the vanguard we will most certainly fulfill.
Or HaChaim
ויאמר בני גד…עבדיך יעשו The tribe of Gad….said: "your servants will do, etc." One difficulty in this verse is the word לאמור. Whom was Moses to tell of their decision? 2) What did they add that they had not previously told Moses in verse 18 already? They themselves had volunteered to do what Moses now demanded of them! 3) Having already said generally: "your servants will do what my lord commands," why did they have to add verses 26 and 27 altogether? 4) Why did they repeat once more: "as my lord has said (verse 27)? Why did the Torah refer to מצוה "commands" in verse 25 whereas in verse 27 it uses the word דבר, "has said?"