I don't think that you are being unreasonable, OP.
I find it quite comical that anybody would think that the Beckham family would have been criticised for not making an ostentatious (and in my view, rather cynical) gesture after the Grenfell fire if they hadn't done so. It would be the last thing on my mind: I wouldn't even think about them if they hadn't publicly associated themselves with it. I certainly wouldn't be thinking, "why haven't the Beckhams told us all about what they are doing for the victims of the Grenfell fire?"
I don't see why this wealthy family, if they wished to make a donation, couldn't do so quietly. But no, they have to be promoting themselves. It's undignified and yes, OP, unseemly.
Why expose your children to criticism when you push them into high profile, public roles that they aren't suitable for? Why not just let them live normal lives? Plenty of children of rich families do.
Brooklyn Beckham is as much a professional photographer as I am, yet his parents allowed him to be exposed to censure as a teenager for pretending to shoot a Burberry campaign. They allowed the second son to pretend to be a model in a Burberry campaign, when clearly he was only hired because of his parents' fame. The third son was releasing a single aged 13 or something, amidst a PR blitz. Why?
I suspect it's because that family have allowed themselves to become the centre of a publicity machine. They collect hangers on who all need to be kept busy and who will continue to suggest opportunities for promotion and publicity because the Beckhams' management company need to earn their 10% somehow, don't they?
Incidentally, Victoria Beckham did not 'come from nothing'. She came from a well-off family.
Anybody who thinks that every celebrity 'giving their time' to causes, or associating themselves with causes, is doing so entirely selflessly is rather naive, I think. Read 'Cause Celeb' by Helen Fielding - the book she wrote before the Bridget Jones books - in which she nails this particular phenomenon far better than I could.