H2B's family from the other side of the world have said they are 90% sure they will not be attending the wedding (will cost £3000 just for plane tickets!). Would it be rude to do the seating plan as if they are not coming? They will be receiving there invite months before everyone back in the UK so can change it before other invites go out.
Dont do this until all rsvps are in.
I wouldn't do your seating plan until you have received responses to your invitations.
Definitely don't do the seating plan until you have received all of your responses. And for the actual seating plan that people look at, we wrote it on the night before and morning of the wedding as people drop out last minute for whatever reason.
I did my seating plan 2 months before the wedding. Then 3 people dropped out. It is now 5 days before the wedding and another guest has bow dropped out. I definitely wouldn't do it far in advance.