1. I wonder who/whom they are speaking to.

2. The expressions they use might depend on whom they are speaking to or how well they know each other.

第一句who/whom都对吧；

第二句，我觉得，这个whom是做介词to的宾语，to提前的话，只能是whom, 即： To whom are they speaking？但现在to没有提前，那么whom有没有受介词on的影响？可以换成who吗？

谢谢！