Who were Alexander's historians that wrote about Indian social conditions?

It is not Sati alone that is mentioned by Aristobolos, the most significant historian that accompanied Alexander to India:

Few reliable records exist of the practice before the time of the Gupta empire (c. 400 CE). Among those that do reference the practice, the lost works of the Greek historian Aristobulus of Cassandreia, who traveled to India with the expedition of Alexander the Great in c. 327 BCE, are preserved in the fragments of Strabo.
_{— Wikipedia: Sati (practice)}

But that already indicates that the 'original' work is lost to us and only inferable through later works.

We do have a collection of ancient Greek writers that write about India:

The main 'official historian' accompanying Alexander would be Ephoros of Cuma's son Demophilus. Another historian, though apparently quite unreliably re-telling many fables would be Onesicritus. Not to discount the other companions of Alexander, though not being historians, they are important as witnesses, like Nearchos. But most direct accounts and works are unknown, leading us back to Aristobulos of Cassandreia:

Greek historian, accompanied Alexander the Great on his campaigns, of which he wrote an account, mainly geographical and ethnological. His work was largely used by Arrian.

The best available source would therefore be the later Arrian and his work Indica, which is available here in an English translation.

As that is not the only source to consider, one may have a slightly more generalised look at Depictions of India in Ancient Literature or a quote-rich Ancient Greek Writers On India And Asia or the scholarly account in:
— U. P. Arora (1982): "Greek image of the Indian society". Μακεδονικά, 22, p470–482. (DOI)

In summary:

Of those who accompanied Alexander to India, Aristobulus, Onesicritus, and Nearchus wrote about the Indian campaign. The only surviving contemporary account of Alexander's Indian campaign is a report of the voyage of the naval commander Nearchus, who was tasked with exploring the coast between the Indus River and the Persian Gulf. This report is preserved in Arrian's Anabasis. Arrian provides a detailed account of Alexander's campaigns, based on the writings of Alexander's companions and courtiers.

Arrian's account is supplemented by the writings of other authors, whose works are also based on the accounts of Alexander's companions: these authors include Diodorus, Strabo, and Plutarch.
_{— Wikipedia: Indian campaign of Alexander the Great}

Which is almost the same list as "The five main sources" for the Wikipedia article Historiography of Alexander the Great. But taken together these still leave some caveats and open desirabilities of quite some importance to consider when reading and interpreting them:

— A. Brian Bosworth: "Aristotle, India and the Alexander Historians", Topoi, Orient-Occident, Vol 3, No 2, 1993 pp407–424. (DOI)

The earliest Greek sources on Alexander offer a rich harvest of ethnographic data concerning ancient India, including customs and traditions of Taxila, marriages, castes etc. However, although belonging to the Indian traditions, the names, figures, social and religious practices they mention often provide us an apparently confusing and incomplete picture. A deeper analysis shows that Alexander’s India as depicted in the fragments at our disposal is used to provide an exotic background to the legendary deeds of the conqueror. In a later period, as well as in the work of many historians who wrote about the life of Alexander, rather than being moved by a genuine interest to discover and describe India, these seem to be moved by different purposes, characteristic of their time. The essay presents some considerations on the work of Arrian and Strabo, with particular reference to the fragments of Aristobulus and Megasthenes.
_{– Stefano Beggiora: "Indian Ethnography in Alexandrian Sources: A Missed Opportunity?", in: Claudia Antonetti & Paolo Biagi (eds): "With Alexander in India and Central Asia Moving East and Back to West", Oxbow Books: Oxford, Philadelphia, 2017. (on jstor)}

— Richard Stoneman: "The Greek Experience of India. From Alexander to the Indo-Greeks", Princeton University Press: Princeton, Oxford, 2019 (on jstor).