Your son is just a little boy and little boys can be a bit defiant. It takes twenty years to raise a child - you have to be patient! If he is disrespectful, you can certainly discipline him, however it's probably going to be more important to give him positive attention and even rewards when you see that he IS behaving appropriately. Both you and your fiance should read my book "Raise Your Kids without Raising Your Voice" because it has lots of strategies for teaching children whatever they need to know, including how to speak and act respectfully. Pay especially close attention to the chapter on The Relationship Rule - this chapter teaches kids how to control themselves when they have negative feelings. If you still need more help, consult a mental health professional or parenting expert in your area.  All the best,
Sarah Chana