I agree, I think younger or other Royals out of the main direct line 'who have no awful baggage attached' could be accepted to work part time and have a career. So, here I mean sorry but being realistic, not the Yorks basically and the very far out family members who's names are known but where never meant to be working Royals unless disaster struck and that won't happen. People hanging around in palaces who don't carry out official duties. The public have an awareness of who the wider family are but more people around than who are doing duties from the much wider family will get people grumbling, which we all see and hear in the press and wider public over the years but I think that in some cases they are very blinkered in their sense of entitlement and lost track of public perception decades ago if they ever had it.
I think anyone of adult age more than 6th in line roughly depending who is what age in the future and where in the family, should be going out to work and especially before or after having young children, they could also do evening and weekend engagements around London or more widely. But having said that Edward and Sophie are vital and Edward is technically, what 10th in line maybe? So it needs to be worked out generation by generation but I think all monarchs grandchildren not in the direct line should start from the position that they will go out to work and earn their own living.
I would say in terms of public events (not the balcony scenes) children and grandchildren of monarchs and children of working Royals in public is fine; behind the scenes, for family parties at Windsor or wherever, yes grandchildren of the actual working Royals (not those just with titles) of course should be there to see what their grandparents have done over the years for the country but not the people chasing the spotlight who are a long way off on the list. I think they don't see what this looks like from afar.
For the balcony; officially working Royals and working Royals children only I would suggest in the direct line or the current and the directly previous monarchs grandchildren (Charles and Elizabeth) only if their parents are working Royals. So Louise and James, studies permitting, or Anne's children but not people further out no matter how nice, because that starts the grumbles. If Sarah Chatto or David started helping part time then them too if they wanted but they don't seem like people trying to get onto a balcony and into pictures ironically which actually makes them better suited in many ways to being there.