Did God foreknow that humanity would fall in Adam?
Yes. The triune God, by their determinate counsel, knew in foreknowledge that the human race would fall in the man Adam. They also knew in that predeterminate counsel that one person of the triune God would have to become a Redeemer.
Les teaches that in eternity past the Father, Son, and Holy Spirit came together and by a determinate agreeing of their three minds decided to create the universe, put planet earth in it, and place the human race on it. They knew in foreknowledge that the human race would fall in Adam, and in that predeterminate counsel they knew one person of the triune God would have to be a Redeemer. That same counsel of Acts chapter 2 moved the whole plan, and by that same triune counsel God has a place waiting for each believer.