I'm not clear why you are pursuing this. Is the idea that the 3 who can't travel will lead to a "free" night to be enjoyed by all 8 people? And that the other 5 will rebook their flights to a day later, to match the tickets flown by the 3? (If so, you will face an uphill struggle getting reimbursed for a party of eight when KLM only needs to pay a reasonable amount for a party of 3)

Or are you willing for the group to split up.and travel separately? (If so, I don't see why the 3 need to spend the extra night at all)