"top" cat acting mad

I have 2 cats that are brothers. They're about 1 year plus 2 months old and always got along.
   
I now have 2 kittens also. They are brothers too. They're about 4 1/2 months old.
   
Now my older male cat is picking on his brother the same age. When he was hissing at the kittens I started loving on him much more, and he calmed down and even was licking a kitten.
   
But he's actually picking a fight {not a whole big fight but attacking a little with the loud YOWLS and all.}
   
His brother doesn't pick fights - he's very laid back and easy-going.
   
Can you help? Thank you, Mary