Kids are NOT adults. Their opinions are uninformed. There is a reason why YOU are in charge and they aren’t. YOU set the standards in your household. YOU decide what is going to happen and what won’t. If you know a course of action is the right thing to do, then enforce it.
When they get old enough to make their own decisions, can verbalize to you why they feel they should be able to do so and so, and you feel they are competent enough to do so, fine.
They need discipline. NO, it is NOT okay that they let it all hang out when they are upset. It is NOT okay that they are rude to you or any other family member. it is NOT okay that they don’t do their best in school. Deal with the tantrums. Be ready to deal with disobedience.
Be firm, and let them know as early as they are able to understand that some behavior will NOT be tolerated.
Kids are more resilient than you think. Let them face the consequences of bad, lazy, defiant, or otherwise undesirable behavior as long as they aren’t directly hurting themselves over the long term. If they don’t get up for school, let them figure out how they will deal with the school.
If they don’t want to practice their sports or dance or music or are half-assing it, or aren’t listening to their teachers in the lessons, then let them experience what it’s like when coach benches them during the big game or they do poorly at that recital or audition for that play they really wanted to be in because they didn’t want to practice or didn’t take it seriously enough.
If they don’t want to eat that meal you made, let them either go hungry or let them fix their own meals, and tell them you will not clean up after them, they are on their own if they get hungry.
If they waste their allowance on stuff you know is bullshit and you’ve told them it’s bullshit, then let them experience not being able to do the thing they want to do because they don’t have the money—don’t give them the money because they cry about it.
Quit doing everything for them. Teach them to keep their rooms clean, to do housework, to care for their personal items like clothing, to prepare their own school lunches basic shit every competent human being has to learn to do. And hold them accountable when they don’t do them. That’s your damn JOB, to prepare your kids for life.