I m seriously not getting his motive
Technically he can't be Anu's half brother coz of his age but his reference of Karn n Arjun was a bit weird n if we go by that dialogue then he is definitely Anu's half brother so i m confused
Regarding ur 2 & 3 point....it can be a possibility
Karn was older than Arjun by 15-16 years, do we know how old is Mr. Bajaj?