My 4 year old is driving me crazy

Janet
My 2nd son was born 12/14... My first is acting out in all kinds of ways! Rude comments, tantrums and testing all the boundaries. Feeling so frustrated and bummed out. We've tried to give him solo time with mom and dad, and help him with the transition but it all seems useless. 
Anyone have tips or tricks to help ease the family into this new chapter?