Gilly you have been given some great advice here already...so what are YOU going to do to change things?
First of all tackle dad....."No dad I am going shopping once a week end of"
Then sister.... "I am going shopping for dad once a week, can you help out the other day"
Then Children " I can do x,y,z but am busy x,y,z.
Unless YOU do something about it, things will never change.
Be kind, but assertive. YOU have a life to lead as well and everyone should not be looking at you to solve ALL their problems. As said though...it has to come from you to stop it all.