Hello @Nikolaos12,
Sorry, in my previous post I referred to an article and then forgot to add the link.
Can I split a reservation payment with other guests?
No, one person doesn't complete the reservation and then add more guests after acceptance by the host.
That way, as you say, that person would be charged the full amount.
If the reservation is an eligible one, the person selecting the listing pays their own share of the cost and then sees the option to invite the other guests to pay.
How does splitting the cost of reservation work?
If the reservation is not an eligible one then you won't see the option to invite others to pay.
Airbnb told me just now that, to be eligible, the reservation has to be
1) for fewer than 28 days
2) for a date 10 or more days away from the date you make the reservation
3) the amount per person must be at least US$1 so 10 guests can't split a reservation that's less than US$10
Steve.