This isn't adivsable, though it has happened in our council, whilst there is possibly no rule against it, take for example if one of the family was to be nominated for postion of chairperson, it wouldn't be appropriate for a family member to nominate or to take part in a vote relating to anyone in their family, this however has happened in some charities where family members have taken part in votes, of course in a council meeting they have to record the votes so they would know who takes part in it. I would say it's inappropriate as they need to be impartial.