Is my older grandson a bad influence?

So i have a 16 year old grand son and an 10 (almost 11) year old grandson, the two are brothers but i feel that the older grandson is a bad influence on his younger brother. the two are very close but the older grandson seems to be having a bad influence. My older grandson rides a Harley and plays in a band which at first wasn't so bad but until his younger brother started copying him, his brother now goes with him on his bike and has come to watch him when he plays at concerts, also the older brother has started to look after his younger brother. they older brother is int that bad but i don't think that its suitable for them to be with each other... would it be possible for me to stop them being together as much? but there parents don't seem to mind when asked. So is my older grandson being a bad influence and why are they so close?