Here's my take, but take it with a pinch of salt ...
I'm not a native!
1. Who do you think is the most important person in your life? I think the most important person in my life is her?? she??Here "
who" is the subject, so you cannot use "
whom". Likewise, in your reply you need "
she" (but I find it too long-winded)
2. Who do you admire? I admire him, so I think we can write "Whom do you admire?" Right?Yes. Strictly speaking, this sentence needs "
whom" because here "
you" is the subject. However, "
who" often replaces "
whom" in informal contexts, so this sentence is fine in spoken, colloquial English.
3. Who do you have next to you now? I have her next to me, so it chould could it be "Whom do you have next to you now?"Yes. Same answer as for sentence no. 2.
4. Who are you eating dinner with in the evening? I am eating dinner with him in the evening today, so "whom" can be used. Right? No. In formal contexts, where you should use "
whom", you also need to move the preposition in front of "
whom".
With whom are you eating dinner in the evening?5. Who do you live with? I live with him, so "whom" can be used. Right? No. Same answer as for sentence no. 4.
With whom do you live?