1)
To whom does "Atem" refer?
1.
Radak: It is you (Shlomo) and Yisrael.
2.
Malbim: It is David and Shlomo; Bneichem are your children. Hashem promised David that his son will be king unconditionally. The stipulation is only for the third generation [and onwards] - "Nishba Hashem l'David