Permissive parenting- opinion please

So my nephew, whom I love a lot is a little over 2 years of age. My son is 8 months old. I love them both dearly. My brother and his wife do not say ‘no’ to anything he does..don’t get me wrong, they totally love their son but believe that stopping him from things will affect his development negatively. He is constantly supervised but if he is breaking and damaging stuff, or throwing food all over the place, throwing tantrums, pushing my son out of jealousy etc., they really do nothing except mildly saying don’t do that and let him be. I know they can parent how they like but my real question is, is this a better way to parent? I already say no to my son for things that may hurt him and let him cry. I also intend to discipline him by saying a firm no in situations mentioned above. Is it better to let a toddler be till they are in school or something and start discipline then? I want to do the best for my son but don’t want to suppress his personality by being a controlling parent. Opinions..?