I'm trying to figure out the difference between Conditional and Subjunctive in the context of describing unrealistic situations. Do I understand correctly that the pairs of expressions below are grammatically correct and have the same meaning?
The first rule of the English subjunctive is "don't use the subjunctive". It is mostly archaic. There are some set phrases and a few situations where the subjunctive may be used. But for the most part, the subjunctive is something to study when you learn Anglo-Saxon, not English.
Now to your sentences. They are all odd.
The first has a past perfect in the condition, "had lived". This is a counterfactual condition. It speaks of a condition that describes a past that did not exist. It is natural to pair this past condition with a "would have" conclusion.
The first example is correct English, but very odd, as there is no natural connection between him living on the moon, and your purchase of a car.
The second seems to be an attempt at a subjunctive. It is not modern English. It probably refers to a future condition, so is different from the counterfactual past tense condition in the first sentence. But as it isn't modern English, it is hard to be sure.
The third sentence seems to use the "should" subjunctive. It doesn't really work. You can form subjunctive sentences "If it should be real". But the first rule says that there are better ways to express this.
The last sentence uses the "were" subjunctive. This is one of the exceptions. It is still fairly common, however you could also say "I wish it was real". Beginners can use "I wish it was real", but advanced learners should also recognise that sometimes native speakers use "were" in this situation.
