For the 'private recordings' of the sort your correspondent seems to be describing a 2.5 thou stylus should be OK. These records were one-off [only one], directly cut, not pressed like commercial records, and were popular for sending messages home from overseas. Many were actually of metal rather than shellac. They are copper colored and extremely noisy no matter what stylus you play them with.  They also don't do ordinary styli a lot of good.  They were intended to be played with miniature thorns or cactus points which wore down quickly to fit the groove. On the other hand if the records are black they are probably 'acetates' (actually a cellulose nitrate lacquer on an aluminum base). You can identify these by peering through the center hole and seeing the metal base. The material is quite soft and damages easily, but a lightweight 2.5 thou stylus should play them OK.

How gramophone records are made: 

The manufacturer cuts a groove in a blank record with a stylus in a cutting-head that vibrates laterally. For commercial issues, the record maker electroplates the cut record and eventually produces a metal negative from which he can press a large number of records. However, for these personal records, he just issues the original cutting. The metal ones are an oddity, and I don't know how easy it was to cut them: certainly the results are quite poor and noisy. Early records were cut in beeswax (which you could electroplate but couldn't play as it was very soft): 'acetates' as I described were introduced from 1935 and are used even today as the first stage in producing LPs. They can be played with a lightweight stylus, though they are fairly soft and so wear out easily.