it is true about Hasan and Husayn; as mentioned in the hadith. Ibn Saád reports from Ímrān ibn Sulaymān; said he: ‘Ĥasan and Ĥusayn are two names from paradise; none of the Arabs knew of this name prior to these two in Jahiliyyah. see here. --- however, the name muHammad was known before the arrival of the prophet sallallahu `alayhi wa sallam. and some christian/jewish scolars who anticipated the prophet, had used these names for barakah/auspiciousness. usually, there is a chapter in sirah books that lists some folk who were named muhammad before the birth of our Master sallallahu `alayhi wa sallam. --- i cannot recall that about the name `ali for the moment.
i heard someone say on tv that the names muhammad, husain [can't remember if they mentioned hasan; i think they did] and ali were unique and no-one had these names before the people who we famously associate them with. sallAllahu 'alaihi wasallam wa radiyAllahu ta'ala anhum. is this true?