Death

During the time of the Prophet (S), literacy was still new in his society, and his people did not have the custom of writing long books. They also did not have as much technology for writing as Muslims did later; for instance, much of the Quran was originally written on non-paper things like pottery shards. So it was not until later that the major Islamic books were written.

Also, there were a lot of things happening (including the need to handle military threats, the expansion of Islam, civil war, sorting out the practicalities of governing, and so forth), and people are more likely to write books when there is more stability. 

It is also quite possible that it didn't occur to some of the people to write a biography. After all, they all knew who the Prophet (S) was, and everything about their society was common knowledge to themselves. Why should they write a book about a subject that everyone knows about?

At the same time, the later companions or those from other regions most likely did not know a lot about the early life of the Prophet (S) because they came into the community later and only saw him in his final years.

Of course many details are passed on in hadith. 

According to hadith, we will see and recognise our relatives in the barzakh.

This is a good question, and one that has received a lot of attention in the contemporary era.

Classically, many Muslims held that death is generally the punishment for apostasy (with some exceptions and conditions). Some Muslims today see this more in line with a modern treason law. That is, today, while killing someone for apostasy is considered a violation of human rights, killing someone for treason against their own nation is considered acceptable. This is because, in the past, religion was a primary marker of public identity and deliniation of the state; whereas, in the modern world, religion is considered a private matter and a matter of personal belief, and national identity is considered primary. 

Also, this law is based on hadith. Some people have challenged the authenticity of hadith that say this, because it seems to go against the Qur'anic view that there should be no compulsion in religion; it also seems unusually harsh, since the Prophet had a merciful and lenient character. Other people hold that it may have been appropriate in the time of the Prophet (where leaving the Muslim community would generally mean militarily aiding the enemy) but it is no longer valid today.

So, basically, one can say that, yes, this is a classical view; but it is still a subject of much discussion.

Also, note that even if the classical law is correct, it is not acceptable for a person to go around killing people because he or she thinks they are apostates. 

There are a number of pieces on this on al-Islam.org, which you can read by going to Google and typing "apostasy al-islam.org".