Need Parenting advice

I grew up with my grandmother always living with us. I resented her my whole life and still don't have fond memories of her and my childhood because she was the third parent who I didn't want her input most of the time. She (was) and my mom is sometimes stern with me son. It makes me feel uncomfortable to hear the way she talks to him, when there are much better approaches. I'm struggling with allowing mainly her, but really anyone in my family "coach, teach, correct" my son when he's doing something they aren't happy with. Is this good for him? To take direction from other adults even when it's not how I would handle it? I try to redirect him when he's acting out, or calmly explaining things to him helps, or giving him choices so he feels in control... Their approach is "no" or "don't" for sometimes no apparent, good reason. It's hard because we live with my parents and it's not like this is a once in a while thing. More like daily. Am I too afraid that he's going to grow up the same way I did? Please help!!