Question

Can a member of a Parish Council sit on a Residents Association ?

Answer 1

Of course, assuming of course that the Residents Association constitution would allow it.  Some residents associations would invite the parish council to nominate a representative in which case the appointment is by the parish council so the individual councillor does not have to declare an interest when in a parish council meeting at which the residents association is discussed (a grant application for example).  If the parish councillor is also a member of the residents association as an individual then most Code of Conduct documents I've seen would require that member to declare an interest when discussing matters relating to the residents association.