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

I think it's normal haha! I've seen this behaviour alot with my niece and nephew. It's their way of testing boundaries with both parents - see who is good cop and who is bad cop. As long as your son doesn't continue with the behaviour as he grows older in the malicious or negative sense, it's nothing to be to in worried about :)