My 4 yrs old boy is highly manipulative and plays favorites with mom and dad. Is this normal child behavior!

Yes, this is very normal. My kids does it all the time! The hubby and I play the good cop bad cop game with them all the time. I feel it is important to have consistent expectations for both parents on what is allowed and what is not allowed. This helps to prevent inconsistencies and the child will know that no means no, no matter who he/she asks.