"All this was to celebrate the first birthday of twins - an occasion which he concedes was more a celebration of the children than for them."
With refer to the above sentence, does it bring out the meaning that the fact of organizing an ostentatious birthday party for children is based on the parents' desire to flaunt the financial capabilities to their classmates, but not for the birthday celebration. Please advise.
Unless the rest of the passage talks about an ostentatious party designed to flaunt their money, no, not at all.
It means the twins were too young to enjoy the party, so it wasn't really for their benefit, but the parents wanted to celebrate the fact that they existed in their lives. It was a celebration OF their existence.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.