What will be a Mokesh for David?
Malbim #1: He will endanger himself due to love for (desire to marry) her.
Malbim #2: According to the opinion that his Kidushin of Meirav was valid, he will sin through marrying her sister.
What is the meaning of "bi'Shetayim Tischaten"?
Rashi, based on Targum Yonasan: [I have two daughters;] you will marry one of the two. The same applies to "Shelosh Anochi Notel Alecha" (2:24:12) - one of the three, like it says there explicitly "choose one of them." Radak - the same applies to "va'Yikaver b'Arei ha'Gil'ad" (Shoftim 12:7). Even though I spoke to you about my two daughters, and it did not work out that you will marry the first, one of them, the latter, will be yours today - you will marry into my family.
Malbim: I did not know about Adri'el's Kidushin of Meirav. I still consent also if you want to marry her; I am connected to you due to marriage due to (my consent for) both of [my daughters].
David's Kidushin of Meirav was valid; Sha'ul wanted to him to sin through marrying her sister "ha'Yom" (in Meirav's lifetime; refer to 18:21:1:2). Perhaps this was Sha'ul's intent, but surely David understood differently. (PF)
