Learn English – What are Could / Can in future Tense

These sentences are actually all in present tense: we often use present tense to express future events.

We can present continuous form getting to talk about things that we are expecting to happen in the future, even if we are not sure exactly when they will happen.

We can also use present simple to talk about future event, but usually we only do this when we are talking about things that are scheduled or timetabled:

David's plane arrives at 07:45
The concert starts at 7pm.

Looking at your first example, about the car, present continuous is better because David getting his car back is not a timetabled event, however you will also hear people using present simple for this kind of dialog.

The second example is somewhat confusing because you use the word can which means is able to. Assuming that's what you meant, here is the question and answer.

Do you think that Blaire can get pregnant again?
No, I don't think that she can.

If you wanted to ask whether it is likely that Blaire will get pregnant again, I think that the future simple is better:

Do you think that Blaire will get pregnant again?
I don't think that there is a chance that Blair will ever get pregnant again.

Yes, absolutely. If you are talking about things that happened at two different times, you certainly can use different tenses to refer to them.

Side note: "America" is a proper noun, and so you shouldn't use an article. For the second part, you probably mean that he will arrive on time. And "vocation" means your job or life's mission; I think you meant he went on "vacation". So the sentence should be, "Although Jason went to America last week for vacation, he will arrive at work on time tomorrow." (Assuming I'm understanding your intent.)