to get the airdrop we only need to hold the BNT token but I want to ask if there are at least how many tokens we have to hold and what is the comparison to get it?
No minimum.
All holders will receive 10% of whatever their BNT balance is at the time of the snapshot.
So if you hold 100 BNT during the snapshot, you will be airdropped 10 ETHBNT.