Death

Here are a few narrations on this topic:

Imam al-Sadiq (A) said, “The things which enter a person’s grave are ritual prayer, fasting, hajj, charity, good deeds, supplication, and its reward is written for those who do them and for the deceased.” (Man la yahduruhu al-faqih)

Imam al-Sadiq (A) said, “Whoever of the Muslims does a good deed for a deceased person, God will double his reward and benefit through it the deceased” (Bihar al-Anwar citing Uddat al-Da’i)

It is related that a man came to the Prophet (S) and asked, “My mother has died. Will it benefit her if I give charity on her behalf?” He said, “Yes.” (Musnad Ahmad)

Apart from Wahhabis who object to this because they see everything as bid'ah, it is hard to see the objection to this since if one is doing something good in the hopes that it would benefit the deceased, at least one is doing something good and beneficial. 

Maybe some people might object because some things are done for esaal-e-sawab which are not overly beneficial in the present time, for instance, printing Qur'ans and distributing them in an area where Qur'ans are easily accessible. This would have been very beneficial in earlier centuries but today because printing is cheap, it often is not the most beneficial thing to do even if it is meaningful, or sometimes things could even be wasteful. So it is good to think about what is most beneficial, and I am sure the deceased appreciate being remembered in a good way!

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.