well in dmc1, dante was 29, 20 years before that, demons attacked his home and killed his mother, they also supposedly killed his brother. 9 years later in dmc3, he meets vergil again. i personally dont think that dante see's vergil as a brother at this point in time, just like how he doesnt think of sparda at this point in time. so dante thought he didnt have a brother, and maybe he only realized it afterwards. that may be why trish said that