If there are multiple passengers on my bookings, do I have to make an offer for all passengers?

Yes. If there are multiple passengers in a booking, the offer amount will be multiplied by the number of passengers including children in the booking. If your upgrade is accepted, all passengers will be upgraded. If you wish to make an offer separately, you will have to contact Customer Care and request for the booking to be split. Otherwise, all passengers in the same booking have to be upgraded together.