No. The advice in the passport, in the back is that you 'should insert particulars of two relatives or friends who may be contacted in the event of accident', Nothing about next of kin, and no order, just advice.
Use a pencil, so that you can change the people or addresses easily without making a mess or tippexing, or a post-it note. Trouble with a post-it not is that it may become detached and lost 'in the event of accident' and the helpful information for rescuers and hospitals abroad, lost.