I think there are good explanations for much of this.
Presumably Pippa wore what she wanted on her big day. I guess she could be called either too conservative or too brazen whatever she wore, someone or other wouldn't like it.
There seems to be a dusky pink or peach theme. If the boys were in pink trousers, then that would be even more embarrassing for them at teenagers than the colour that was chosen. The gold/beige colour goes ok with the pink.
No doubt Kate didn't want to upstage her sister. I don't see what is inappropriate about her outfit.
and so on.
Not a royalist at all, but I guess they are human at the end of the day.