Are you saying that the 9th May is your annual parish/town council meeting where the Chair is elected? If that is the case, there has been arguments in the past on the interpretation of the notice required to call this election. As the new council come into existence on the 7th May, some argue that you still need to give the 3 clear days notice (although lack of notice doesn't illegitimise the meeting). Others argue that the annual parish / town council meeting has to be called within 14 days of the election and that is all the notice needed. The assignment of committees is not a legal requirement for the annual parish / town council meeting as not all councils have committees.
The attendance at the 9th May meeting would be the newly elected Councillors, not the old council and there would be a requirement for them to have signed their acceptance of office forms in advance of taking their seats.