Hey,
I think all of us are facing somewhat similar problems. I do not have any siblings and hence depend on my cousins to help. My elder cousin who is a guy, is less than helpful and the rest of the gals, are not helping in anything. My HTB's rather busy with his own work. I did most of the things on my own, except for printing of the invites and mailing address. The rest are done by me, including my simple montage.
I guess, between HTB and us, we need to be really understanding. Maybe for us, they see things in a big picture, they tend to forget the details and us, being gals, details matter alot. So, the best will probably be, tell the HTBs specifically what needs his attention. In that case, it saves the friction. =)
As for helpers and siblings, i guess, they will tend to be like that. Its our wedding, they will rather be "outsiders" No choice. Well... Got to be positive and tell ourselves, its ok if they don't want to help and not willing to help, when its their turn, they will understand how it feels to be all alone... Meanwhile, we got to be strong and positive!
SO JIAYOU! ALL BRIDES! WE CAN DO IT! =) Stay positive.