My child doesn't listen?

Okay so it has been brought to my attention that my four year old son( July will be 5) has a problem listening to other family members, myself& his father included... I noticed it before when u tell him to do something and if he doesn't wanna do it he won't!!   I always brushed it off as Oh he's just a four year old but when a family member mentioned something I realized I need to take control of the situation and try to correct it before it gets too bad!! Does anyone else have this problem?? What are some ways you went about correcting it.. he is currently in preschool and I have never had a complaint once so is he just spoiled from being a only child and just acting out in front of family? I'm really upset someone else brought this to my attention and I desperately need advice on how to get him to listen when someone tells him to do something!! Thank you mommas<3