G.B.
He has some points so don't totally discount him, just because he is focusing on looks and appearance. They are not the all in all but they do influence who wants to be nice or mean to us.
Every person judges people on how they look and act. If a man who is dirty and smells bad and is talking to himself sits next to you are the public park are you going to sit there and visit with him? Get up and move? Ignore him and try not to gag from the stench? Yell for the kids to run quickly to the car?
You have made a judgement on him based on appearance and actions.
I think the same as you as far as clothes for school. Safety and health come first then they can wear whatever they want after that.
The kids should be picking out the clothes with you. They could pick out the whole weeks worth of outfits on Sunday evening but in my house they change moods to often to do it more that the night before.
Tell him to do this with you so that he can see their faces and how they go about making the choices. That may allow him to input some choices and make him feel involved. He might only need to do this a few times so he gets the feel of how it's handled by you.
Once he is educated on what is acceptable or not he may lighten up.