Learn English – Should I use “like” or “likes” with “some”

Will is ordinarily not used in if clauses to signify mere futurity. It is used only in a handful of situations:

• If it is employed in the sense of be willing (to VERB)—or, in the negative, refuse (to VERB):

  If you'll get beer, I'll make hamburgers. If you won't get beer, I'm not going to make hamburgers.

• If it is employed emphatically with the sense of insist on VERBing—again, the negative has the sense of refusal:

  If you will ask silly questions you must expect silly answers.
  If you won't follow instructions you must expect failure.

• If it is employed to signify that you accept a prior prediction as fact—here the negative implies a negative prediction:

  If (as you say) your mother will be here tomorrow, we'd better get clean sheets for the spare bedroom.
  If (as you say) your mother won't be here tomorrow, there's not much point in getting clean sheets for the spare bedroom.

Consequently, unless what you're speaking about involves one of these situations, you want to use do:

If {you don't / he doesn't} leave tonight we can go out for ice cream.

—But as the commenters point out, we're more likely to use BE going (to) here than bare do.

The second, as the subject "Bob and Alice" is plural. The adverb doesn't change that.

It would, of course be possible to rephrase "Bob drives a BMW and Alice (drives) a Lexus". The repeated verb can be dropped.

The adverb "respectively" is sometimes misused, even where it is grammatically correct. Grammarist.com gives examples of good and bad use of "respective".